Step by Step Guide to OVERHAULING GENERATORS on Ships

marineinsight.com
“A Step-by-Step Guide To Overhauling Generators”
Publication date: January - 2025 (Second Edition),
Author: Anish Wankhede
Published by: Marine Insight LLP
Design – Marine Insight Copyright © 2025
NOTICE OF RIGHTS
All rights reserved. No part of this book may be rewritten,
reproduced, photocopied, stored in a retrieval system,
transmitted or distributed in any form or means, without prior
written permission of the publisher.
NOTICE OF LIABILITY
The authors and editors have made every eﬀort possible to
ensure the accuracy of the information provided in the book.
Neither the authors and Marine Insight, nor editors or
distributors, will be held liable for any damages caused either
directly or indirectly by the instructions contained in this book, or
the equipment, tools, or methods described herein.
1

Dedicated To All
Marine Engineers
2

About the Author
Anish Wankhede is the co-founder of Marine Insight, the world’s
largest online maritime education platform, dedicated to
improving the knowledge and skills of seafarers globally.
A certiﬁed AI leader, management-level marine engineer, and
sought-after speaker, Anish has devoted his career to advancing
maritime education. His extensive work has helped countless
maritime professionals navigate the evolving demands of their
industry.
Anish has authored numerous highly regarded technical ebooks,
oﬀering practical insights into essential marine engineering and
operational topics. Widely used by seafarers and marine
engineers around the world, his resources are trusted for their
clarity and relevance.
Anish Wankhede
3

Preface to the Second Edition
The maritime industry continues to evolve at a rapid pace, and
with it, the expectations placed upon marine engineers have
grown immensely.
Overhauling a ship's generator is not just a technical task—it is a
cornerstone of a vessel's operational reliability, efficiency, and
safety.
Since the first edition of this ebook was published, we have
received valuable feedback from marine engineers, technical
superintendents, and students worldwide, enabling us to refine
and expand the content to better meet the industry's needs.
In this second edition, we have included updated practices,
enhanced diagrams, and step-by-step instructions to address
modern challenges encountered during generator overhauls.
Recognizing the increasing focus on environmental compliance
and energy efficiency, we have added a dedicated section on
maintaining generators for optimized fuel consumption and
reduced emissions.
Additionally, this edition features real-world case studies that
highlight common pitfalls and solutions, making it a practical
guide for professionals at all levels.
We have also expanded the troubleshooting section, providing
clearer explanations and detailed diagnostic steps to help
engineers confidently address unexpected issues during
overhauls. Understanding that time is critical aboard a vessel,
4

this edition emphasizes eﬃcient planning, teamwork, and safety
measures to ensure successful overhauls in even the most
challenging conditions.
It is our hope that this edition continues to serve as a valuable
resource, empowering marine engineers to excel in their roles
while contributing to the safe and eﬃcient operation of their
vessels.
We remain deeply grateful to the global maritime community for
their ongoing support and encourage readers to share their
feedback and experiences to help us improve future editions.
Fair winds and smooth seas,
5

Index
1. INTRODUCTION
2. PRE-PLANNING
3. PREPARATION
4. OPENING/ DISMANTLING OF PARTS
5. CLEANING AND CHECKS
6. MEASUREMENTS AND CALIBRATION
7. CLOSING AND ASSEMBLING
8. ALTERNATOR MAINTENANCE
9. STARTING PREPARATION
10. RUNNING IN
6

Chapter One
Introduction
The main power source on most ships is its electrical power
generator engine, popularly known as the "Heart of the Ship."
Without these power generators, it’s impossible to operate any
engine room, deck, or bridge machinery.
A wide range of marine generators is used on board ships,
depending on the vessel type, power requirement, and, of
course, the owner’s budget preferences.
Marine engineers working on ships are required to understand
the construction and working of these power units in order to
carry out maintenance and repair works.
7

Additionally, a thorough knowledge of generator-specific safety
protocols, spare part management, and troubleshooting
methods is essential to avoid unexpected breakdowns during
voyages. Such expertise ensures the operational reliability of the
vessel under challenging conditions.
Though the type and look of generators vary from ship to ship,
the procedures for their overhauling and maintenance almost
remain the same.
Understanding the environmental implications of generator
performance is also becoming increasingly important. Issues
such as fuel efficiency, NOx and SOx emissions, and compliance
with MARPOL Annex VI are critical in modern ship operations.
Thus, marine engineers must align their maintenance practices
with these regulatory requirements to ensure sustainable
operations.
What is D’carb or Major Overhauling of
Generators?
D’carb is a technical term used in the marine industry for
cleaning and maintenance of engines. The process includes
removal of carbon particles, which are deposited on the internal
parts such as the piston, liner, cylinder head assembly, etc., as a
result of long hours of continuous operation.
Carbon buildup and worn-out parts reduce combustion
efficiency and increase fuel consumption. By performing D'carb,
the generator’s fuel efficiency, power output, and overall
performance are restored.
8

D’carb is also carried out when the generator parts have
completed their running hours, an accident or breakdown has
occurred, or while preparing for Continuous Survey Machinery
(CSM). The process involves the renewal of running parts such
as bearings, rings, etc.
In recent years, advanced maintenance strategies such as
predictive maintenance using vibration analysis, thermal
imaging, and digital monitoring systems have gained
prominence. These technologies enable engineers to
proactively identify wear and tear, ensuring timely D’carb
procedures without compromising ship schedules.
This guide helps both aspiring and experienced marine
engineers working on ships in learning the correct and
sequential procedure for carrying out major overhauling of
generators or auxiliary engines.
9

The guide has been categorized into different sub-processes,
each explaining an important part of the D’carb procedure.
Important Terminology - Generator
To better understand this e-book, let’s learn some important
terms which will be frequently used throughout the guide.
D’carb or De-carbonization: A non-technical term used when
the combustion chamber of the generator—which includes the
piston, liner, rings, cylinder head, valves, etc.—is cleaned to
remove the carbon deposits accumulated as a result of long
running hours.
Major Overhauling: In technical language, D’carb is known as
“Major Overhauling” of generators, as it includes opening and
maintenance of all important parts, along with cleaning and
inspecting bearings and turbocharger (depending upon the
running hours).
Auxiliary Engine (Generator): Technically, the auxiliary engine,
also known as the Generator, is a combination of a Prime Mover
and an Alternator.
Prime Mover: The mechanical part of the auxiliary engine that
rotates the crankshaft by means of energy generated from fuel
combustion (I.C. engine principle).
Coupling flange: The crankshaft is connected via a coupling
flange to the alternator, which consists of magnets and windings
for generating electricity.
Proper Alignment: Proper alignment between the crankshaft
and alternator is critical during overhauls to prevent
10

misalignment, which could result in vibration issues and
premature wear of components.
Alternator Maintenance: Engineers must verify alternator
insulation resistance, winding integrity, and load-sharing
capabilities as part of the maintenance routine.
Power Distribution: The electricity generated is then carried
through the bus bars to the main switchboard, which distributes
it to all the essential systems of the ship.
Auxiliary Power Management Systems: Used to regulate load
distribution across multiple generators, ensuring redundancy
and optimal power utilization. Familiarity with these systems is
vital for marine engineers to manage power requirements
efficiently during routine and emergency operations.
Compression Ratio: The ratio of the volume of the combustion
chamber when the piston is at the bottom dead center (BDC) to
the volume when the piston is at the top dead center (TDC). A
critical parameter affecting engine efficiency and power output.
Turbo Lag: The delay in power delivery from a turbocharged
engine caused by the time it takes for the turbocharger to
generate sufficient boost. Understanding this is essential for
optimizing turbocharger performance during maintenance.
Indicator Diagram: A graphical representation of the pressure
versus volume in an engine cylinder. Used to analyze engine
performance, detect anomalies, and diagnose problems like
poor combustion or excessive back pressure.
11

Blow-by: Leakage of combustion gases past the piston rings into
the crankcase. Excessive blow-by can indicate worn piston rings
or liner wear and is often identified during overhauls.
Tappet Clearance: The gap between the rocker arm and the
valve stem. Proper adjustment is crucial for efficient engine
performance, preventing valve damage or loss of compression.
Specific Fuel Oil Consumption (SFOC): A measure of fuel
efficiency that calculates the amount of fuel consumed per unit
of power generated. This is monitored regularly to ensure
generators operate within optimal parameters.
Cooling Water Jacket: A chamber surrounding the engine
cylinders or liner where cooling water circulates to maintain
operating temperatures. Any blockage or leakage here could
lead to overheating and engine damage.
Lube Oil Analysis: The process of examining lube oil for wear
particles, water contamination, or fuel dilution. This provides
critical insights into engine health and component wear.
Crankshaft Deflection: The deviation of the crankshaft from its
normal position. Measured using a deflection gauge, this is a
vital check during major overhauls to ensure alignment and
prevent vibrations.
Clearance Volume: The volume of the combustion chamber
above the piston when it is at TDC. Ensuring this volume is within
12

specifications is crucial for maintaining compression and
preventing knocking.
Alternator Excitation System: The mechanism that supplies
current to the alternator field winding to generate the magnetic
field necessary for electricity generation. Faulty excitation can
cause voltage irregularities and should be inspected during
maintenance.
Backlash: The clearance or play between mating gear teeth.
Measured during maintenance to ensure efficient torque transfer
and prevent gear damage.
Insulation Resistance (IR): The resistance of electrical windings
to current leakage. IR testing is a critical step in alternator
maintenance to prevent short circuits or equipment failure.
Power Factor: The ratio of real power to apparent power in an
electrical system. Maintaining a high power factor ensures
efficient use of generator capacity and reduces fuel
consumption.
Piston Ring Gap: The gap between the ends of a piston ring
when it is fitted in the liner. Correct gaps prevent blow-by and
ensure proper sealing.
Running Clearance: The gap between two moving parts, such
as between a bearing shell and a crankshaft journal. Maintaining
the correct clearance prevents excessive wear and overheating.
13

Cylinder Head Torque Values: The speciﬁc torque applied to
bolts securing the cylinder head to the engine block. Incorrect
torque can lead to gas leaks or head damage.
Governor Droop: The decrease in engine speed as load
increases, controlled by the governor to ensure stable operation
across load conditions. Essential for load-sharing between
generators.
Emergency Stop Device: A manual or automatic mechanism to
shut down the generator in case of emergency, such as
overspeed or loss of lube oil pressure. Its operation should be
tested regularly.
CSM: The Continuous Machinery Survey (CMS) system is
important to ﬁnd out the condition of the machinery/equipment
by opening up a part of the machinery following reasonable
procedures in a continuous and systematic manner.
14

Chapter Two
Pre-Planning
Before opening a generator for a major overhaul, it is essential
to perform thorough pre-planning.
The pre-planning phase ensures that the operation is conducted
safely, eﬃciently, and with minimal risks. Proper preparation
reduces the likelihood of delays, accidents, and unanticipated
costs.
15

1. Power Availability
Before commencing the overhaul, ensure that sufficient power is
available onboard to sustain essential operations. In the event
that one generator is taken out of service, backup power
sources must be readily available to maintain normal operations.
The overhaul should be scheduled at a time that allows for
flexibility in case of any unforeseen breakdowns.
2. Special Tools
Verify that all special tools required for the overhaul are
available, in good condition, and ready for use. Special tools may
include spanners, torque wrenches, lifting equipment, hydraulic
jacks, and more.
If any tools are missing or require replacement, arrange for them
to be sourced ahead of time.
- MAN Diesel & Turbo Generators
Ensure the availability of specialized bearing extraction tools,
injector testers, and hydraulic tightening systems. For larger
MAN engines, confirm that the crankshaft deflection gauge is
calibrated, as these units require precise alignment due to their
size and complexity.
- Wärtsilä Generators
Wärtsilä engines require customized jacking bolts and piston
installation tools. Also, confirm that tools for inspecting the
turbocharger, such as nozzle ring gauges and rotor balance kits,
are in working condition.
16

YANMAR Generators
- YANMAR-speciﬁc torque wrenches and valve seat extraction
tools are essential. Check the condition of the provided lifting
equipment for pistons and connecting rods, as YANMAR engines
often utilize lightweight but specialized hardware.
- Cummins Generators
Cummins models often require digital calibration tools for
injectors and ECM resetting equipment. Make sure to have fuel
rail pressure testers and turbocharger vane actuator alignment
kits available.
3. Measuring Tools
Accurate measurement is crucial during an overhaul. Ensure that
all required measuring and gauging tools are available,
calibrated, and in optimal condition. This includes micrometeres,
vernier callipers, dial gauges, and deﬂection gauges. Any tool
with zero error should be recalibrated, as inaccurate
measurements could lead to improper assembly or failure of
components.
MAN engines often have stringent clearance tolerances. Ensure
that advanced bore gauges for liner calibration and precise
inside micrometers for crankshaft journal measurements are
ready for use.
Wärtsilä engines require specialized tools for measuring tappet
17

clearance and fuel pump cam wear. Include a surface roughness
tester to assess cylinder liner glazing.
- YANMAR Generators
Inspect small-end bush clearances using YANMAR’s specific
tapered pin gauges. Use custom inside diameter tools for liner
and piston ring groove measurements.
Cummins engines demand injector height gauges and
crankshaft end-play testers. Ensure the availability of calibration
equipment for ECM sensors to confirm accuracy.
4. Spare Parts
Take inventory of the spare parts available on board and ensure
that critical components such as bearings, seals, gaskets, and
piston rings are readily accessible. If necessary spares are not
available, initiate requisitions to ensure they are received in time
for the overhaul.
Stock MAN-specific piston ring sets, cylinder liners, and
turbocharger nozzle rings. Check the availability of electronic
components for their advanced control systems, such as sensor
modules and actuator assemblies.
Keep spare Wärtsilä-certified cylinder heads and valve kits
onboard. Include gaskets for their LNG or dual-fuel systems, as
well as spare cooling water jackets due to their frequent use in
Wärtsilä engines.
18

- YANMAR Generators
Ensure the availability of YANMAR’s proprietary big-end bearing
kits and connecting rod bolts. Additionally, stock
high-temperature O-rings for exhaust manifolds.
Cummins engines require spares such as injector tips, fuel filters,
and ECM-compatible wiring harnesses. Confirm the presence of
exhaust after-treatment system components, especially for Tier 3
or Tier 4 engines.
5. Power Pack (If Applicable)
In certain ship types, especially those equipped with refrigerated
cargo, power packs may be kept onboard for emergency power
supply. If such equipment is available, check that it is in working
condition and properly maintained.
6. Team Preparedness
All personnel involved in the overhaul operation should be
well-informed of the procedure and their specific roles. The team
must have a clear understanding of the tasks, the sequence of
operations, and the safety precautions involved.
A briefing should be conducted to discuss the generator’s
specific model, the manufacturer’s manual, and the overhaul
plan.
7. Understanding Safety Protocols
Safety protocols ensure that overhauls are conducted without
harm to personnel or equipment. Following brand-specific safety
19

measures can further enhance the reliability and safety of the
process.
● Safety Interlocks: MAN engines feature advanced interlocks
to prevent accidental starts. Always verify the correct
engagement of the shaft locking device before beginning
maintenance.
● Oil Circuit Protection: Ensure that lube oil supply lines are
isolated carefully to prevent backflow. MAN systems may
have additional non-return valves that must be checked for
functionality.
● High-Temperature Areas: Use heat shields when working
near MAN turbochargers, as their designs concentrate
heat.
● Electronic Safeguards: Wärtsilä engines are equipped with
automation panels (e.g., UNIC systems). Confirm that all
electronic alarms are deactivated and logged before
isolating the engine.
● Fuel Switching Protocols: For dual-fuel engines, follow
Wärtsilä's prescribed steps to ensure safe isolation of LNG
lines, including depressurizing the gas system.
● Turbocharger Precautions: Turbocharger casing in Wärtsilä
units should be purged and inspected for unburnt fuel
before disassembly to avoid fire hazards.
- YANMAR Generators
● Compact Design Safety: YANMAR’s compact layouts make
access challenging. Double-check isolation points for fuel
20

and cooling systems to avoid accidental spills in tight
spaces.
● Torque-Induced Risks: YANMAR generators often require
precise torque for fasteners. Ensure calibrated torque
wrenches are used to prevent bolt failures under load.
● Rotating Part Cautions: Always check for residual rotational
inertia in ﬂywheels or shafts even after isolation.
● Electronic Monitoring Devices: Cummins generators rely
heavily on ECM (Electronic Control Modules). Disable ECM
safety overrides to avoid accidental starts during
maintenance.
● Exhaust After-Treatment Safety: For Tier 4 models with
after-treatment systems, conﬁrm the absence of residual
DEF (Diesel Exhaust Fluid) in the system to prevent
chemical exposure.
● Sensor and Wiring Isolation: Disconnect all sensors and
wiring harnesses to avoid short circuits or unintended
electrical activation.
8. Signs and Symbols
Know the sign plates over generators which indicate safety of
machine and operator. Know them correctly.
21

9. Documentation and Checklists
Proper documentation and comprehensive checklists ensure
systematic execution of the overhaul process, reducing errors
and oversight. Tailoring these for specific engine makers
ensures alignment with their standards.
● Documentation: Include a detailed log of bearing
clearances, crankshaft deflection readings, and
turbocharger performance parameters. MAN-specific forms
for shaft alignment and wear-down readings are crucial.
● Checklists: Ensure entries for hydraulic jack settings,
cylinder liner calibration values, and sealing ring conditions
are recorded. Add a pre-operation test for the advanced
vibration sensors installed in MAN systems.
22

● Documentation: Wärtsilä recommends maintaining a history
of fuel injection timings, valve clearances, and UNIC
automation diagnostics. Record deviations from standard
operating parameters and calibrate after completion.
● Checklists: Include steps for inspecting LNG handling
systems, checking electronic actuator feedback loops, and
ensuring air cooler cleanliness. Wärtsilä manuals also
emphasize recording tappet and camshaft wear
measurements.
- YANMAR Generators
● Documentation: Log measurements for speciﬁc
components such as big-end bearings and valve guides.
YANMAR engines often require precise records of piston
ring groove wear and liner ovality.
● Checklists: Ensure all tools, such as hydraulic jacks and
lifting devices, are pre-tested and their operation
documented. Include detailed steps for inspecting the fuel
injection system for carbon deposits.
● Documentation: Cummins systems require detailed ECM
logs, including fault codes and parameter adjustments.
Document calibration data for injector ﬂow rates and
turbocharger actuator settings.
● Checklists: Include entries for verifying exhaust
after-treatment components, wiring harness continuity, and
sensor calibration. Cummins manuals highlight maintaining
23

a checklist for alternator coupling inspections and ECM
reset procedures.
10. Preparing for Advanced Troubleshooting
● Vibration Analysis: Incorporate guidelines on identifying
abnormal vibrations in the generator post-overhaul,
including the use of vibration meters and spectrum
analysis.
● Electrical Fault Diagnostics: Include a section on diagnosing
alternator issues such as grounding faults, insulation
failures, and excitation system problems.
11. Generator Performance Optimization
● Discuss techniques such as maintaining optimal fuel
injection timing, ensuring proper turbocharger operation,
and regular cleaning of air and fuel systems.
● Highlight steps to reduce NOx and SOx emissions,
including fuel adjustments and use of cleaner alternatives.
12. Digitalization in Generator Maintenance
● Explore the integration of digital tools for real-time
monitoring of generator parameters like load, RPM, and fuel
consumption.
● Discuss the use of maintenance management software to
track performance data and predict failures before they
occur.
13. Sustainable Maintenance Practices
● Oﬀer guidance on properly disposing of used oils, ﬁlters,
and worn-out components in compliance with MARPOL
regulations.
24

● Encourage periodic energy eﬃciency audits to identify and
mitigate unnecessary power losses.
25

Chapter Three
Preparation
For carrying out a zero-error, cent-percent safe d'carb
procedure, it is very important to take out suﬃcient time for
planning and preparation, considering important safety aspects
and following the correct procedure for the same.
Preparing a generator for overhaul not only includes selecting
the right tools and gauges but also involves choosing the correct
sequence of operations and isolation.
For a safe and smooth d'carb, the following preparation needs to
be done without fail:
26

Isolation
Before opening any machinery, it is essential to isolate it ﬁrst.
Failure to do so may lead to oil spills, injury, or accidents.
For isolating an auxiliary engine, two separate parts of the
machinery—the Alternator and the Prime mover—need to be
isolated.
Follow the steps below:
● Isolate the power supply from the alternator to the bus bar
by opening the Air Circuit Breaker.
● Isolate the power supply for the Lube Oil Priming Pump.
● Isolate the Lube Oil supply to the prime mover.
27

● Isolate the cooling water supply to the prime mover (also
for Jacket and Lube Oil Cooling).
● Isolate the Fuel Oil supply.
● Isolate the Starting Air supply to the prime mover.
● Ensure to list all the valves and supplies that are closed as
a checklist to reopen once the maintenance is ﬁnished.
● Disconnect the electronic control panels, including engine
management systems (EMS) and automatic voltage
regulators (AVR), to prevent accidental damage during
mechanical operations.
● Disconnect temperature, pressure, and vibration sensors to
avoid electrical feedback that may harm the engine
monitoring system.
While operating or closing any of the valves to the generators,
especially cooling water and fuel oil valves, operate them slowly
and in the correct sequence so as not to ﬂuctuate the pressure
of other running generators.
Procedure for Operating Cooling Water Valves:
● Close the line valves on the top of the prime mover coming
from the expansion tank.
● Close the inlet valve slowly so as not to disturb the
pressure of other running generators.
● Close the outlet valve.
Procedure for Operating Fuel Valves:
● Close the fuel inlet valve to the engine.
● Close the fuel outlet valve after the pressure gauge shows
the minimum value.
28

● Check the fuel pressure of the line and other generators.
● Ensure electronic injectors and fuel control modules are
properly isolated and stored in anti-static packaging to
prevent damage from static electricity.
Once the alternator and prime mover are completely isolated,
start draining the jacket water by opening the drain valve and
vent cock on the J.C.W outlet line.
29

While doing so, keep an eye on the expansion tank level, as a
sudden decrease in the tank level indicates leaky water valves
(outlet or expansion cock valves).
Tagging Out
Tagging out is a process carried out as an additional safety
measure while the overhauling work is in progress.
If tagging out is not followed, any person may accidentally switch
on the breaker of any power equipment associated with the
generator under maintenance or operate any valve of the
system, leading to a serious accident.
30

Checks on Special Tools
For every large machinery, the maker always supplies various
sets of special tools to open/close its parts.
These special tools may include:
● Special spanners
● Tools for opening injectors or starting air valves
● Tools for opening cylinder heads
● Tools for overhauling cylinder heads (e.g., removing
inlet/exhaust valves or seats)
31

● Tools for inserting pistons
● Liner holding and removing tools
● Tools for opening main/crank pin bearings
● Hydraulic jacks, hydraulic pipes, connections, and pumps
● Torque wrench
● Correct size I-bolt, D-shackle, and rated chain block with
rated capacity
● Special tools for opening and lifting turbochargers
● Stands for T/C rotors and pistons
● Electronic micrometers and dial indicators for precise
measurements of clearances and tolerances.
This is not an exhaustive list but a brief description of special
tools that must be checked before starting the maintenance
operation. Many other special tools may be added depending on
the generator's make.
All such special tools must be checked for freeness and correct
operation. Hydraulic jacks and pumps must be pre-operated to
check for any kind of leakage.
32

Operating Procedures of Tools
While handling any machinery, one must know the proper
operating procedure. The same rule applies to the special tools
used to dismantle or retighten the generators on ships.
Diﬀerent parts of the generator, such as the cylinder head, liner
piston, etc., require the usage of separate tools in the correct
order.
By knowing the handling procedure of tools, one can easily
assemble/disassemble various parts of the auxiliary engine with
utmost ease.
33

Mentioned below are examples for the correct usage of
generator tools to avoid problematic situations while doing
major overhauling of the ship’s auxiliary engine or generator.
Example 1: Liner Drawing Tool:
Liner drawing tool seems very simple to use, but wrong usage of
the same has lead to liner stuck or drawing/ inserting of liner
diﬃcult at times.
When using such tools one should know the use of the centre
plate provided with the nut.
Never keep the centre plate or bar loose as it keeps the entire
tool in the centre position of the liner, which means when
34

drawing out or inserting the liner from the jacket of the
generator, chances of the liner getting tilted and stuck reduces.
Ensure that the centre line of the tool is coinciding with the
centre line of the liner.
Example 2. Protecting ring tool:
The protecting ring located in the top portion of the liner is
removed by a special tool. Some generator makers have
Anti-Polishing ring located in the top portion.
The anti-polishing ring (APR) in a 4-stroke marine engine liner is
ﬁtted ro remove carbon deposits from the upper part of the
35

piston to prevent carbon buildup, reduce liner wear, improve
piston ring sealing, and enhance combustion efficiency.
It is different from a protecting ring, which serves a broader
purpose of shielding parts from wear or heat rather than
focusing specifically on carbon removal.
After cleaning of the contact surface for the removal tool is
rested on the frame and the insert/ backup plate is inserted
either at the bottom of the protecting ring or in the groove
provided in the ring, depending on the generator's design.
It is important to secure the tool with the generator's frame
through securing bolts, else the tool may slip out leading to an
accident.
36

If the protecting ring is badly stuck and the removal tool is
excessively tightened, the ring may break, making it more
diﬃcult to remove from the liner with the help of the removal
tool.
Operation of Hydraulic Jack
The correct operation of a hydraulic jack system is critical for
ensuring the safe and eﬃcient loosening or tightening of nuts
during generator overhauls. Hydraulic jacks provide the
high-pressure force required to stretch studs and release nuts
on large machinery, but their misuse can lead to equipment
damage or accidents.
37

The hydraulic jack system typically includes the hydraulic jack
unit, spacer rings, hydraulic pump, and associated piping.
The following steps to be kept in mind for operating the
hydraulic jack system eﬀectively.
● Cleanliness of Components: Ensure that all parts, including
the hydraulic jack, stud threads, and nut surfaces, are clean
and free of grease, dust, or metal shavings. This prevents
sticking and ensures smooth operation.
● Oil Quality and Level: Use only the recommended grade of
clean hydraulic oil. Fill the hydraulic pump to the marked
38

level, and avoid overﬁlling as this may cause spillage during
operation.
● Hose and Connector Inspection: Check all hoses for cuts,
cracks, or weak spots. Ensure that connectors are free of
corrosion and are properly secured to avoid leaks under
high pressure.
● Seal Integrity: Inspect the hydraulic jack seals for wear or
damage. Replace worn seals to prevent oil leakage during
operation.
● Pressure Gauge Calibration: Verify that the hydraulic
pump’s pressure gauge is calibrated accurately to provide
reliable readings during operation.
● Purging: Before use, purge the hydraulic jack by opening
the purging screw located on the top of the unit. This
removes trapped air from the system, ensuring consistent
force during operation.
● Securing the Jack: Position the jack body over the cylinder
head studs. Tighten the jack body securely, ensuring there
is no gap between the sliding surfaces of the jack and the
stud.
● Spacer Ring Alignment: If spacer rings are used, align them
correctly to avoid uneven force distribution during
operation.
● Controlled Pressure Application: Gradually apply pressure
using the hydraulic pump. Do not exceed the maximum
rated pressure for the jack or the stud, as indicated in the
generator’s manual.
● Avoid Over-Tightening: Rotate the jack anti-clockwise
(open) by 3/4 of a turn after reaching the desired pressure
to ensure the nut does not stick inside the jack while the
stud is being stretched.
39

● Leakage Check: Continuously monitor for oil leakage
around the jack or hoses. If leakage occurs, reduce the
pressure slowly, stop operation, and replace the seals or
faulty components immediately.
● Pressure Stability: Ensure the pressure remains stable
during the operation. Any sudden drop may indicate a leak
or an improperly purged system.
● Gradual Pressure Release: After loosening or tightening the
nuts, reduce the jack pressure slowly to prevent sudden
movement of the jack piston, which could cause it to stall
inside its liner.
● Component Cleaning: Once the operation is complete,
clean the hydraulic jack, hoses, and ﬁttings with a lint-free
cloth to remove residual oil or debris.
● Storage: Store the jack and pump in a clean, dry location,
and cover them to protect against dust and humidity.
Before applying pressure through pumps, ensure jacks are
purged by opening the purging screw on top.
Tighten the jack body over cylinder head studs and purge till
there is no gap between the sliding surface of the jack. Tighten
the purging screw and rotate the jack anti-clock wise (Open) by
3/4th of a turn.
This is done to avoid the nut from sticking inside the jack when
the stud is stretched by hydraulic pressure and the nut is rotated
in open direction.
40

If there is any leakage of oil, pressure must be reduced
immediately but slowly without operating it further. Rectify the
leakage and renew seals within the jack if required.
Torque Wrench
A torque wrench is a specialized spanner designed to apply a
precise amount of torque to a fastener, such as a nut or bolt.
It ensures that components are tightened to the speciﬁcations
provided by manufacturers, thereby preventing under-tightening
41

(which can lead to loosening) or over-tightening (which can
cause damage to components or threads).
Steps for Using a Torque Wrench:
- Understand the Specifications:
○ Refer to the equipment manual or technical
documentation to determine the correct torque value
for the fastener.
○ Check the unit specified (e.g., Newton-meters (Nm),
foot-pounds (ft-lbs)) and ensure it matches the scale
on the torque wrench. If the units differ, convert the
value using a reliable conversion formula or calculator.
- Adjust the Torque Wrench:
● Rotate the handle or dial to set the desired torque value on
the scale. For analog wrenches, ensure the scale indicator
is precisely aligned.
● For digital torque wrenches, input the required torque value
directly into the device.
- Prepare the Wrench:
● Attach the appropriate socket or adapter to fit the fastener.
● Secure the connection to prevent slippage during
operation.
- Position the Torque Wrench:
● Place the socket over the fastener and ensure the wrench
is perpendicular to the fastener axis.
● Avoid using an extension or adapter that could alter the
applied torque unless calibrated for such configurations.
42

- Apply Force Gradually:
● Apply steady, even pressure to the handle without sudden
jerks or excessive speed.
● Stop applying force when the torque wrench emits a click
(in click-type wrenches) or a digital indicator signals that the
set torque has been reached.
- After Use:
● Reset the torque wrench to its lowest setting after use to
maintain calibration.
● Store it in a clean, dry place to prevent rust or damage.
- Common Types of Torque Wrenches
● Click-Type: Produces an audible click when the desired
torque is reached.
● Beam-Type: Displays the torque value on a scale as force is
applied.
● Digital/Electronic: Provides precise digital readings and
may include additional features like memory or alarms.
● Split Beam: A durable alternative to the click-type, often
used in high-torque applications.
- Safety Tips
● Inspect the torque wrench before each use for damage or
wear.
● Avoid dropping the tool, as impacts can aﬀect calibration.
● Use gloves when working in environments with slippery or
hazardous conditions to maintain a ﬁrm grip.
43

Values and Units
An auxiliary engine is a high-speed rotating machine comprising
several heavy-weight parts connected using stud bolts and nuts,
which are either torque or hydraulically tightened.
These components play a critical role in the safe and eﬃcient
operation of the engine. Proper tightening ensures structural
integrity, while improper tightening can result in catastrophic
failures.
If any part becomes loose or is not tightened to its rated value, it
can lead to devastating outcomes such as:
● Mechanical Failures: Breakage of studs or bolts during
operation, leading to disassembly of key components.
● Explosions: Accumulated stresses can cause sudden,
explosive failures, endangering personnel and equipment.
● Operational Downtime: Unplanned maintenance delays
caused by failures, leading to ﬁnancial losses and potential
voyage interruptions.
Several such incidences in the past have resulted in casualty
and loss of property.
44

Understanding Tightening Values and Units
Every auxiliary engine part has specific tightening values that
must be adhered to during assembly or reassembly. It is
essential to:
● Know the Manufacturer’s Specifications: Always refer to the
engine manual for accurate tightening values for studs,
bolts, and nuts.
● Understand Unit Conversions: The tightening values are
often provided in units such as:
○ Torque: Typically in kgf-m (kilogram-force meter) or
N-m (Newton meter).
○ Hydraulic Pressure: Commonly measured in kg/cm²
(kilogram per square centimeter) or MPa (megapascal).
● Convert Units When Necessary: Ensure proper conversion
if the tools being used operate on different units. For
instance:
○ 1 kgf-m = 9.80665 N-m
○ 1 MPa = 10.2 kg/cm²
Critical Best Practices
● Calibrated Tools: Always use calibrated torque wrenches
and hydraulic pumps to ensure precision. Periodically verify
their calibration to avoid inaccuracies.
● Cross-Reference Values: Double-check the tightening
values in the maintenance manual against the tool settings.
Mistakes in units or values can lead to over-tightening or
under-tightening, both of which are hazardous.
45

Avoiding Errors
● Label Tools: Clearly mark torque wrenches and hydraulic
equipment with the units they measure to avoid confusion.
● Training and Awareness: Ensure all team members are
trained to interpret values and convert units accurately.
● Reference Tables: Keep conversion charts readily available
for quick reference during overhauls.
Tightening values for MAN Generator with units
46

By thoroughly understanding the importance of values and units,
marine engineers can ensure a safe, eﬃcient, and precise
overhaul process, safeguarding both personnel and equipment.
47

Chapter Four
Opening/ Dismantling of Parts
Opening the auxiliary engine for de-carbonization (D'carb) is a
critical maintenance procedure and is typically performed based
on the company's policies and the manufacturer's running hour
recommendations for diﬀerent components.
Adhering to these guidelines ensures eﬃcient operation and
prolongs the life of the machinery. Proper planning and
understanding of the engine's condition are essential for
minimizing downtime and avoiding unnecessary repairs.
48

Key Considerations Before Opening the Auxiliary
Engine
Running Hour Thresholds:
● Cylinder Head and Piston Rings: These components have
shorter running hour intervals as they are exposed to high
thermal and mechanical stresses.
● Cylinder Liners and Connecting Rods: Longer intervals are
permissible as these are less susceptible to wear when
maintained correctly.
● Bearings: Main and connecting rod bearings generally have
the highest operational hour range, but regular inspection
for metal fatigue or uneven wear is crucial.
Planned vs. Emergency Overhauls:
● Planned maintenance follows the speciﬁed schedule,
ensuring parts are replaced or inspected systematically.
● Emergency overhauls may require all major parts to be
opened due to incidents like crankcase explosions,
overheating, or abnormal vibrations.
Machinery Attached to the Generator:
● Turbochargers, fuel pumps, and lube oil pumps have their
own maintenance schedules and may not align with the
main engine overhaul. These should be inspected for signs
of fouling, imbalance, or wear during the D'carb procedure.
49

Enhanced Sequence for Opening Generators
After taking the necessary safety precautions and completing
pre-operational checks, the following generalized sequence is
followed:
1. Open Rocker Arm Cover, Crankcase, and Cam Case Doors
2. Disconnect Cylinder Head Connections (Water, Lube Oil,
Injector, etc.)
3. Remove Fuel Pumps and Connections to the Cylinder Head
4. Loosen Cylinder Head Torque/Hydraulic Nuts
50

5. Remove Cylinder Head
6. Remove Protecting Ring (if Provided)
7. Remove Big End Bolts and Bottom Connecting Rod Shell
8. Remove Piston
9. Remove Camshaft Bearings
10. Remove Main Bearing
11. Timing Gear Inspection
Turbochargers, lube oil, and cooling water pumps can be
opened based on their respective schedules or operational
requirements. They often require specialized procedures
outlined in the manufacturer’s manual.
Components removed should be cleaned, inspected, and stored
in a clean, safe environment to avoid contamination or damage
during the maintenance process.
Open Rocker Arm Cover, Crankcase and Cam
case doors
Opening the Rocket arm cover: The rocker arm cover protects
the rocker arms and associated components, such as pushrods,
valve springs, and the cylinder head area, from debris, dust, and
oil splashes.
51

Procedure:
● Use a spanner or wrench of the correct size to loosen and
remove the retaining bolts on the rocker arm cover. Keep
the bolts organized for easy reassembly.
● Carefully lift the cover to prevent damage to the gasket or
the cover itself.
● Inspect the gasket for wear or damage. Replace it if
necessary to ensure a proper seal during reassembly.
Opening Crankcase Doors: The crankcase doors provide
access to the internal moving parts of the engine, such as the
connecting rods, crankshaft, and bearings. They are used during
inspections, maintenance, and troubleshooting.
52

Procedure:
● Ensure the engine is shut down and the crankcase
ventilation is adequate to release any trapped gases.
● Isolate the engine from any fuel or electrical sources to
ensure safety.
● Use a torque wrench or spanner to loosen the securing
bolts or clamps holding the crankcase door in place.
● Carefully open the crankcase door, ensuring that it does
not drop or damage the hinges. Use appropriate tools if the
door is heavy.
Open Cam Case Doors
The cam case houses the camshaft, tappets, and associated
mechanisms for valve operation.
Accessing this area is essential during timing adjustments,
camshaft inspections, or tappet clearance checks.
Procedure:
● Ensure no residual pressure is present in connected
systems.
● Use the appropriate tool to loosen and remove the
retaining fasteners securing the cam case door.
● Exercise caution to avoid damaging the gasket or sealing
surfaces.
● Detach the cam case door carefully and place it on a clean,
ﬂat surface. Avoid scratching or contaminating the sealing
surface.
53

Removal of Cylinder Head
Cylinder head nuts may be tightened by hydraulic pressure or
torque wrench depending upon the power rating/size of the
prime mover. Hence for opening the same, you may be required
to use a hydraulic jack or pneumatic/ mechanical spanner.
After opening water connections, lube oil connections, air
connections etc. ensure that the head is free from other parts.
Use the hydraulic jack as described in the “operating procedures
for tools” section.
Once all the nuts are loosened, remove and mark them for unit
number and position. Most of the cylinder heads have an
54

arrangement where the lifting tool can be attached only after
removing the fuel valve.
Hence jack out the fuel valve and insert the lifting tool. After
removing the nuts, clamp the head lifting device and with a chain
block lift the cylinder head and rest it on a wooden base to avoid
damage to the seating surface.
Always ensure that the lifting equipment used has the correct
capacity for the load to avoid accidents or damage to
equipment.
55

Removal of Cylinder Head Parts
Removal of Valves
● Use a valve spring compressor tool to compress the valve
spring and remove the cotters (two identical halves locking
the valve with the spring assembly).
● Detach the valve rotator and lift out the valve carefully.
Ensure the cotter pairs for each valve are not intermixed
and are kept in labeled containers or marked positions to
avoid confusion during reassembly.
● Inspect the valve for wear, pitting, or bending. If damage is
found, replace it with a new one as per the manufacturer’s
speciﬁcations.
56

● Clean the cotters, springs, and rotator to remove carbon
deposits or debris that could interfere with the valve's
functionality during reassembly.
Removal of Seat
● Inspect the valve seat for scoring, cracks, or uneven
contact with the valve. If found defective, proceed with
replacement.
● Makers often provide specialized tools for jacking out the
valve seat. Attach the tool securely and follow the
operating instructions for safe removal.
● If no tools are available, an alternative method is to weld
(pad welding) an iron plate or old valve to the seat. Rapidly
quench the weld with water to loosen the seat, then use a
hammer and rod to drive it out carefully.
● After seat removal, inspect the seat pocket for debris or
damage. Clean and verify alignment to ensure proper
seating of the new valve seat. Use a dummy seat to check
the correct alignment and tolerance.
Removal of Valve Guide
● After removing all valves and springs, clean the valve guide
area thoroughly using a solvent like diesel or kerosene to
remove carbon, soot, or oil deposits.
● Place the cylinder head in a working stand to provide
stable access.
● Using a mandrel or an undersized brass rod, punch out the
valve guide from the bottom (valve) side. Strike evenly to
avoid damaging the cylinder head.
57

● Inspect the bore for scoring or cracks. Clean the bore and
measure it to ensure it meets the required tolerance for a
new guide.
Removal of Starting Air Valve
● Remove starting air valves in situ (on the engine) or after
removing the cylinder head, depending on accessibility.
● Use a starting air valve jacking tool provided by the engine
manufacturer. Tighten it securely to the valve and jack it out
smoothly.
● Service or replace damaged components as needed to
prevent leaks or failure during operation.
58

Removing Piston, Connecting Rod, and Big End
Once the head is out of the generator frame, preparation for
removing the piston can be carried out. The piston can be drawn
out by means of an I-bolt, screwed on the top of the piston, that
is connected to a chain block of rated capacity.
Piston Removal After Removing Head
The piston and connecting rod are tightened to the big end
either by hydraulic/torque-tightened studs (oblique cut
connecting rod in two parts—YANMAR, MAN, SKL, etc.) or by tie
olts (connecting rod in 3 parts such as big two-stroke
engines—DIAHATSU, SULZER, etc.).
59

Depending upon the make:
● Either only the piston is removed from the top without
opening the bottom end (3-piece connecting rod), or
● First, the bottom end is dismantled, followed by the removal
of the piston (for 2-piece connecting rods).
Fire Rings or Piston Cleaning Rings
Most generators are equipped with ﬁre rings or piston cleaning
rings (also known as protecting rings) on the top of the liner for
cleaning carbon deposits on the upper area of the piston, i.e.,
the piston land. These rings prevent carbon deposits from
entering the liner bore during piston operation.
60

Inspection and Cleaning:
● Before removing the piston, ensure that all carbon deposits
are cleaned. This prevents excessive force being required
to move the piston and reduces the risk of damage to the
liner surface.
● Use a wire brush or scraper to clean deposits around the
piston crown carefully.
Removing the Fire Ring:
○ Engage the turning gear (if provided) or manually turn
the engine to a position (typically 80–90 degrees
before TDC) where the ring can be easily accessed.
○ Use a ﬁre ring removal tool or a jacking tool as per the
manufacturer’s guidelines to disengage the ring.
61

○ Ensure the tool is securely attached during this
operation to prevent slippage or damage to
components.
Steps to Remove Piston and Connecting Rod
After removing the ﬁre ring, turn the engine to get access on the
top part of the piston i.e piston is around TDC.
● Removing the Piston:
○ Screw an I-bolt into the threaded hole on top of the
piston crown.
○ Attach the I-bolt to a chain block or lifting tackle of
adequate capacity. Slowly and carefully lift the piston
vertically out of the liner.
○ For larger engines, ensure the cylinder liner is
protected from scoring by using guide plates or
sleeves during piston extraction.
○ Place the removed piston, connecting rod, and big
end cap on a clean wooden base or support to
prevent damage.
62

○ Avoid stacking components and label them for proper
identification during reassembly.
Removing Piston With Oblique Cut Connecting Rod
If there are only hydraulic/torque tightened studs in the big end
(as provided in oblique cut-two piece con-rod), they have to be
opened first before removing the piston.
Depending upon the size of the prime mover, it may be required
to use a chain block and wooden plank to support the big end
once the stud nuts are opened.
A threaded i-bolt hole will be provided in the big end housing for
support.
Turn the crankshaft till the con-rod bolts are accessible for
opening and removing the bottom housing (30 Deg after TDC or
as prescribed in the manual). Take weight of the piston by a
chain block from top as shown in the figure.
Use hydraulic jack as described in “Operating procedures for
tools” section after checking the rated pressure of the big end
nuts.
Once the nuts are loose, support the big end by chain block,
rope, wooden plank etc., whatever is convenient to take out the
bearing.
Take little weight on the top chain block to hang the piston and
lift the piston by 20mm.
63

While removing the bottom half of the con-rod, tie the bearing
shell to the half with a piece of cloth to avoid falling or slipping
inside the crankcase.
Before removing the bottom bearing shell and bottom support,
mark it with a permanent marker or by stamping.
After getting some space, remove the upper shell and mark it as
“U” along with a unit number to avoid mixing up.
Install minimum two liner holding tools before removing the
piston as a stuck piston may cause liner to come out from the
jacket space.
64

Once the connecting rod is free to remove, rotate the crankshaft
such that the web goes free of the con-rod upper half
simultaneously taking the piston weight on the top chain block.
As the crankshaft is free of con-rod, start lifting the piston with
the chain block and avoid damaging the crankpin surface.
Remove piston and keep it on the piston stand table. Mark or
stamp the unit number from where it is drawn out.
Removing Piston Three Piece Connecting Rod
Some generators are equipped with three piece straight con-rod
like those found in Diahatsu, Sulzer etc. (And are similar to two
stroke marine engine).
For removing the piston in such models, it is not necessary to
remove the hydraulic bolts of the connecting rod. The piston is
attached to the crank pin housing of the connecting rod by
means of tie bolts, which are generally torque tightened. Make
sure to check the torque settings against the manufacturer's
speciﬁcations before proceeding.
65

For removing the piston, open the cross wire lashing from the tie
bolts. Follow the same procedure as described above for
removing protecting ring and cleaning i-bolt hole, carbon
deposits etc. before removing the piston.
Turn the engine so that the piston of the concerned unit is at
BDC and with the help of torque wrench, open the tie bolts.
Remember to mark the bolts as per their positions of removal.
With piston at BDC, ﬁt i-bolt and chain block on top. Start lifting
the piston and ensure that the liner is secured with the liner
holding tool. Once the piston is out along with the half part of
66

connecting rod and is rested on the stand, prepare to remove
the the crankpin bearing assembly of the con rod.
Before opening the bottom end hydraulic bolt, make
arrangement to support the bottom end housing either by chain
block, rope or log of wood placed below the housing (resting on
both the sides of the crankcase door).
Double-check the stability of the supporting arrangement to
ensure that the housing does not drop or shift unexpectedly.
Turn the big end assembly to 90 degree with respect to its TDC
or BDC position as it will be easy to access the hydraulic nuts
67

through crankcase door. Insert hydraulic jack assembly over the
nut and apply rated pressure.
Once the nut is loose, remove the jack after removing the
pressure completely from the system. Handle the hydraulic jack
carefully, ensuring that the rated pressure is neither exceeded
nor abruptly released to prevent equipment damage or injury.
Be careful not to drop housing or bearing shell inside the
crankcase. Use cloth or rag to tie up the shell with the body to
avoid dropping of the same.
Once the bottom end bearing housing is out, ensure to cover the
crank pin with a cloth to avoid any scratches on the same.
Inspect the crank pin surface for any signs of scoring or damage
while it is exposed, and document its condition for maintenance
records.
Also cover the liner opening with a hard board from top to avoid
any tools or dust from falling inside the crank case or on crank
pin.
Additionally, ensure that all removed parts are properly cleaned,
labeled, and stored to facilitate eﬃcient reassembly and avoid
mix-ups.
Piston Ring Removal
Once the piston is out of the generator, keep it in a piston stand.
Remember that the edges of the piston ring are sharp enough to
cause cuts to your skin; therefore, wear gloves while removing
them.
68

If a ring removal tool is provided (such as a spreader with a
spring), use it and start from the top ring. If no tool is available,
you can use synthetic ropes (two pieces) on both corners of the
ring and then spread the ring by applying outward force.
Once the ring is clear from the groove, draw it out from the
piston.
Piston Pin Removal / Connecting Rod Detachment
The connecting rod is attached to the piston with a piston pin. To
remove the connecting rod, the piston pin must be removed ﬁrst.
69

For easy removal of the pin, turn the piston upside down with
the top face resting on a wooden plank.
Hold the connecting rod with a rope to avoid misbalance or
tipping oﬀ the complete assembly. This step is crucial to maintain
stability during the removal process.
Further, two small pieces of wood can be inserted in the void
space between the rod and the piston to make it stiﬀ while
removing the connecting rod from the piston.
70

With a snap ring plier, remove the circlip that holds the pin inside
the piston. Once the circlip is out, support the connecting rod
with a rope for easy removal of the pin by taking the con-rod
weight oﬀ of it.
As the pin comes out, ensure that you carefully guide it to
prevent any damage. The connecting rod can then be lifted out
of the piston and kept on a separate wooden plank for
safekeeping.
71

Liner
Liner of a generator is removed when it completes its running
hour as prescribed by the manufacturer or when it has worn out
and has cracks.
Some generators are equipped with liner holding jacket which is
connected to the liner by means of 'O' rings.
It is not necessary to remove these holding jacket in order to
take out the liner. However, as liners are generally removed after
a long running period, it is advised to remove the jacket prior to
removing the liner.
This is done to prevent O'ring in this area from making the liner
removal diﬃcult and time consuming.
Before attempting liner removal, ensure that all associated
components, such as cylinder heads and pistons, have been
72

safely removed and properly secured. Double-check for any
residual pressure in the cooling system that might interfere with
the removal process.
Liner removing tool is provided with a jacking arrangement to
pull out the liner from the jacket. When removing the liner, ﬁrst
clean the seating surface of the liner.
Use liner removing tool which is attached on the top and bottom
part of the liner and which can be jacked out by tightening the
nut provided in the tool.
Ensure not to apply excess force if the liner is not coming out
even by jacking. It may lead to bending or breaking of liner
removing tool.
73

Inspect the liner holding jacket for any signs of damage,
corrosion, or wear before proceeding with its removal. Replacing
worn-out O-rings during this process is highly recommended to
avoid future leaks.
If such situation arise wherein the liner is stuck, use
unconventional methods such as- make arrangements to cool
the liner (by blanking the bottom and pouring ICE), or by using
hydraulic jack from the bottom.
Both these methods may only be used if the liner is badly stuck
in the jacket and not coming out by using the liner removing tool.
When using ice, liner has to be fully covered by ﬁlling up to the
bore area (combustion chamber). Put a plate at the bottom of the
liner so that ice cannot go into the crankcase.
Once the liner is cold, remove it by using the removing tool. (Due
to low temperature, liner will shrink leading to removal of the
same). After removing the liner, thoroughly clean and inspect the
liner seat and the holding jacket for cracks, pitting, or other
forms of damage.
When using hydraulic jack, be absolutely sure not to damage
crankshaft or any other part of the generator. The hydraulic jack
is to be put in such a position that it may help in removing the
tool to pull out the liner (apply jack below the removing tool
resting on a plate leveled either on the door or the web).
Use removing tool and hydraulic jack pressure together to
remove the liner and never apply excessive hydraulic pressure if
the liner is still not coming out as it may damage the crankshaft
or the engine frame.
74

It is good practice to measure the liner's bore and compare it
with the manufacturer's speciﬁcations to conﬁrm if the liner was
indeed worn beyond acceptable limits. This data can be useful
for maintenance records and troubleshooting.
Main Bearing
Main Bearing For overhauling the main bearing, it is not
necessary to open any other part. The crankshaft where the
main bearing is attached can be bottom supported or under
slung type.
First open the side bolts near the crank case doors in
underslung type. Special tool is provided to open and support
the bearing keep so that the bearing shell can be
held/supported or removed.
75

Ensure the working area is clean and free from oil or debris to
prevent slipping and ensure worker safety. Keep caution while
removing the accessible keep i.e., top keep for normal
supported crankshaft or bottom keep in case of underslung
crankshaft, so as to prevent slipping of the bearing shell in the
crankcase.
Turn the crankshaft so that you have enough space to put
hydraulic jacks over the main bearing keep bolts. Inspect the
hydraulic jack and tools for proper functioning before use to
avoid operational delays.
Once the accessible keep is removed along with the shell, as the
other part is ﬁxed, the other shell is removed by rotating the
shaft and using a shell pull-out tool, which is a small “T” shaped
tool inserted in the oil hole.
76

While using the shell pull-out tool, ensure the tool is properly
secured to avoid damage to the bearing shell or crankshaft
surface. Lubricate the bearing surface slightly to ease shell
removal and avoid scoring.
For normal bottom-supported crankshaft, a bearing keep lifting
tool is provided.
For underslung crankshaft, keep holding tool is provided, which
ensures that the keep should not fall inside the oil sump. After
removing the bearing shells, thoroughly inspect for wear,
scoring, or heat marks.
Any damage should be documented, and the shell should be
replaced if necessary. Clean the crankshaft journal and bearing
housing with lint-free cloth before assembly to ensure proper
ﬁtment.
Thrust Bearing
The thrust bearing is normally mounted on the forward-aft of the
main bearing, which is on the ﬂywheel side, to accommodate
axial thrust of the crankshaft.
The thrust bearing metal also comes in two parts - upper and
lower. The lower part is normally attached with the main bearing
keep with knock pins. Removal of the thrust bearing can easily
be done while opening the main bearing.
During an auxiliary generator engine overhaul, it is critical to
carefully inspect the thrust bearing for wear and damage.
77

Begin by securing the engine to prevent accidental movement of
the crankshaft. Ensure all necessary safety precautions, such as
locking out the engine and isolating the fuel supply, are in place
before proceeding.
To access the thrust bearing, follow these steps:
1. Remove the engine covers and ensure the crankcase is
adequately ventilated to avoid any accumulation of
ﬂammable gases.
2. Drain the lubrication oil to a safe level to avoid spills or
contamination during the process.
3. Dismantle the main bearing cap carefully, taking note of the
orientation of each component for reassembly.
4. With the main bearing removed, the lower thrust bearing
can be detached by releasing the knock pins and sliding it
out. The upper thrust bearing can then be inspected by
carefully rotating the crankshaft to expose it for removal.
Once removed, thoroughly clean the thrust bearing and its
housing, and check for any signs of scoring, pitting, or excessive
wear. Replace the thrust bearing if necessary, ensuring the
replacement matches the manufacturer's speciﬁcations.
Apply clean engine oil to the new bearing surfaces before
installation. Reassemble all components in the reverse order,
double-checking clearances and alignment.
78

Gears
The engine comprises several gears, which transmit the rotary
motion from the crankshaft to the pumps and camshaft. The
location of the gear train is at the opposite end of the ﬂywheel or
alternator.
The camshaft then operates the governor drive and also
incorporates fuel pump and valve drives. The main gears in the
engine are the Crank Gear, Idle Gear, and Cam Gear, which drive
all the pumps and are free from the crank or camshaft. The cam
gear operates the governor drive.
Crank Gear:
Removal of the crank gear is normally done by the maker's
technician when there is a major problem and when the gear has
to be replaced. The normal procedure for removal of the crank
gear is:
● As the crank gear is ﬁtted on the crankshaft, the gear
assembly has to be loosened by drilling a hole at the
bottom land of the gear.
● Insert a chisel through this hole to loosen the gear
assembly.
● Draw out the crank gear carefully.
Additional Tip: Always check for wear and tear on the crankshaft
spline and replace damaged parts to avoid future failures.
79

Cam Gear:
● Remove the timing gear case cover.
● Remove the governor from the body.
● Remove the governor drive gear. Ensure that no load or
thrust is applied on the same beforehand.
● Normally Allen bolts are provided to power-lock the
governor drive with the cam gear. Open the same with an
Allen key of the proper size.
● Put a strong wire rope in the holes provided in the cam
gear body and draw out the gear from the timing gear
inspection cover with the help of a chain block.
● Additional Tip: Ensure the alignment of timing marks on the
cam gear and crank gear is noted before removal to avoid
reassembly errors.
Removing Idle Gear:
● Before removing the idle gear, all related drives must be
removed ﬁrst.
● Remove all the pumps (lube oil, cooling water, fuel oil, etc.)
ﬁtted on the drive.
● Open the timing gear cover/gear case.
● If a tachometer is attached on the same side, remove it.
● Remove the cam gear before removing the idle gear.
● Remove the idle gear mounting bolts and, with the help of a
wire rope, draw out the idle gears.
● Additional Tip: Inspect idle gear bushings and mounting
bolts for deformation or excessive wear and replace them
as necessary.
80

Camshaft:
● Remove the cam gear drive and cam gear shaft with it.
● Ensure the fuel pump and fuel tappet are out from the top
of the camshaft.
● Ensure inlet/exhaust valve drives (push rods) are removed.
● Remove the starting air rotary valve from the end.
● Camshafts are tightened together by bolts; open them and
remove the camshaft in parts from the anti-flywheel side.
● Additional Tip: During reassembly, ensure proper
lubrication of camshaft bearings and check for axial and
radial clearances to maintain optimal operation.
Attached Parts
Attached pumps
Attached pumps, such as lube oil, jacket water, or fuel pumps,
are critical components in the overhaul of marine auxiliary
generator engines. The following procedure outlines the steps
for removing and servicing these pumps effectively:
● Before disassembling any pump, ensure proper marking of
all parts to facilitate reassembly. This is crucial for
maintaining the integrity of the system and avoiding
confusion during reinstallation.
● Remove all piping attached to the pumps. This includes
disconnecting hoses and any fittings that may obstruct
access to the pump.
● Open the cover by removing the bolts and nuts. Use
appropriate tools to avoid damaging any components.
81

● Remove the seal cover and the mechanical seal. Inspect
these seals for wear, as they are vital for preventing leaks.
● Open all bolts of the bearing cover and remove the outer
bearing. Ensure that you keep track of all fasteners.
● Take out the rotary portion of the mechanical seal and
remove the rotor and rotor housing, which gives access to
draw out the inner rotor and shaft. This step is critical for
accessing internal components that may require
maintenance or replacement.
● Proceed by removing the inner bearing and the collar. Be
cautious during this process to avoid damaging
surrounding parts.
● Additionally, while handling pumps, check for any signs of
wear or damage on all components, including bearings and
seals. If any parts are found to be defective, they should be
replaced immediately to ensure optimal performance after
reassembly.
● After disassembly, clean all parts thoroughly using
appropriate solvents and methods to remove any
contaminants or buildup that could aﬀect performance. This
is especially important for fuel pumps, where precision is
critical for proper operation.
Once all components have been inspected, cleaned, and
necessary repairs made, reassemble the pump in reverse order,
ensuring that all seals are replaced with new ones to prevent
leaks upon reinstallation.
82

Flywheel Coupling
The connection between the prime mover and the alternator in a
marine auxiliary generator engine is crucial for efficient
operation. This connection is facilitated by a flywheel, which can
be secured using either fitted bolts or isolation rubber and bolts.
Regular maintenance checks on these components are essential
to ensure optimal performance and safety. After a certain period,
it is important to check the tightness of the fitted bolts or the
condition of the isolation rubber. Opening of Isolation Rubber:
● Remove the flywheel cover.
● Engage turning gear and rotate the flywheel so that access
and removal of bolts is easy.
83

● Once the bolt is loose, carefully remove the attached
rubber.
● Slowly rotate the ﬂywheel and take all rubber pads and
bolts.
In addition to these steps, it is vital to inspect the condition of the
ﬂywheel itself for any signs of wear or damage. During
reassembly, it is advisable to apply a thread-locking compound
on the bolts to prevent loosening due to vibrations during
operation. This precaution helps maintain tightness over time,
reducing maintenance frequency.
Governor:
Before removing the governor, it is very important to measure
the distance and angle of the linkage arm from the governor
84

connection to the rack connection when the engine lever is at
stop position. Drain the oil from inside of the governor. Remove
the wiring and connections coming from the control room which
regulates the synchro- motor on top of the governor.
Open the foundation bolts of the governor and lift the governor
out of generator frame and keep it in a wooden plank.Ensure not
to damage the shaft which sits on the slot of the driving
assembly.
Air Cooler
The air cooler unit is mounted on the generator after the
turbocharger and before the scavenge air box.
Before opening the air cooler, ensure:
● All pipes and connections are removed from the cooler.
85

● Arrange chain blocks and attach them such as to make
easy the removal of the cooler unit
● Start opening the securing bolts on the frame of the cooler
to detach it from the generator
● Once all the bolts are loosened, take load on the chain
block and remove all the bolts and draw out the cooler
element carefully
● Jack the cooler through jacking holes and bolts if required
● Keep the unit in a wooden plank and clean the element by
using chemicals
86

Chapter Five
Cleaning and Checks
After opening up major parts, thorough cleaning and checks
must be performed on diﬀerent components of the generator.
This ensures optimal performance and minimizes the risk of
failures during operation. Proper documentation of all
inspections and replacements is also critical.
Cylinder Head & Mountings
Cylinder head
● For cleaning the cylinder heads, it is advised to keep them
submerged in water for at least 2-3 hours.
● A mixture of water and carbon-removing chemical can
enhance the cleaning process. Ensure the solution is
prepared as per the manufacturer's recommendations.
● Pressure test of the cylinder head should be conducted by
plugging all the cooling water inlets and ﬁlling the head
completely with water.
● When the arrangement is done, supply air to the head from
the cooling water outlet with a pressure of +2 to 3 bar of
jacket cooling water pressure of the generator.
● Observe carefully for any signs of water leaks, cracks, or
weak spots in the cylinder head during the test. Any
defects should be repaired or replaced as required.
87

● Lapping of the valve seat and checking the general
condition of the seating surface of both the valve and the
seat should be carried out.
● During lapping, ensure uniform contact between the valve
and seat. An uneven surface could lead to improper sealing
and loss of compression.
88

Starting Air Valve
● Check the condition of the spring for its tension. Replace
the spring if it shows signs of fatigue, deformation, or wear.
A weak spring can lead to unreliable operation of the air
valve.
● Check the surface of the seat. Lap it if required.
● Ensure the seating area is smooth and free from pitting or
corrosion to maintain an airtight seal.
● Apply anti-corrosion coating if advised by the manufacturer.
Fuel Injector
● Overhaul the fuel injector by cleaning all the parts in diesel
or kerosene oil.
● Check for carbon deposits around the nozzle tip and clean
thoroughly.
89

● Use lint-free cloths for drying the components after
cleaning to avoid introducing contaminants into the system.
● Check the condition of the spring, especially in generators
using heavy oil, as springs tend to seize and break under
prolonged exposure to high operating temperatures.
Inspect the spring's dimensions using a micrometer to
confirm they meet specified tolerances.
● After assembling the injector, check and set the fuel valve
for its opening pressure using a fuel injection testing
machine.
● Record the set pressure and ensure it aligns with the
manufacturer's specified range. Repeat the test multiple
times to ensure consistency.
● Additionally, inspect the nozzle holes for clogging or
uneven spray patterns.
● Clean or replace the nozzle as necessary to ensure optimal
atomization of fuel.
Relief Valve and Indicator Cock
In most of the generators, indicator cocks and relief valves are
integrated together.
● Check for cleared holes and leaky cock seat by blowing air
from one side.
● Check for lifting pressure of the relief valve as prescribed in
the user manual.
● Inspect the overall condition of the relief valve housing for
cracks or signs of wear that may compromise functionality.
90

● Ensure proper lubrication of moving parts within the relief
valve assembly to avoid sticking or operational failure.
● Test the relief valve's operation under simulated load
conditions, if possible, to conﬁrm its reliability during actual
engine operation.
Exhaust, Inlet Valve, and Springs
● Check for signs of sulfuric acid corrosion and bends on the
exhaust/inlet valve stem.
● Check for high-temperature corrosion of the valve poppet.
● Check the seat and valve for scoring and blow-by marking.
Do valve lapping if required.
91

● Use a borescope to inspect areas of the valve seat that are
not easily visible, ensuring thorough examination.
● Valve Seat Corrosion & Scoring: Check the spring for
tension by bouncing it on a flat plate and measuring its
length after compression.
● Measure the free length and compressed length of the
valve spring using a caliper or micrometer to verify that it
meets the manufacturer’s specifications.
● Inspect the valve guide clearance for wear or elongation,
which can lead to improper valve seating.
Piston
● Clean the top surface and piston land with a buffing
machine or wire brush to remove carbon deposits from the
same.
● Do not use a metal brush or buffing machine on the lower
part of the ring grooves or piston skirt, as it may be coated
with a special compound.
● Clean the bore for the gudgeon pin and clear the oil holes
provided for cooling and lubrication by air.
● Clean piston ring grooves with rough paper dipped in
diesel oil for efficient and fast results.
● Examine the piston crown carefully for any signs of
micro-cracks or thermal fatigue caused by high operating
temperatures.
● Verify the condition of the ring grooves for any warping or
excessive wear that might affect the piston ring's
performance.
92

● Use an ultrasonic thickness gauge to measure the piston
crown thickness, ensuring it is within allowable limits.
● Inspect the oil scraper ring for proper fit and ensure it is not
clogged or worn, which could lead to increased oil
consumption.
● Conduct a thorough dimensional check of the piston skirt
to confirm it matches the manufacturer's tolerances, as an
oversized or undersized skirt can cause operational
inefficiencies.
93

Liner
● Clean the liner with diesel oil.
● Clean the O-ring grooves of the liner thoroughly, ensuring
no residue or deposits are left behind.
● Check for cracks, scoring marks, or pitting surfaces on the
liner. Use a ﬂashlight or borescope to inspect hard-to-see
areas for hidden cracks or irregularities.
● Check for mirror polishing or glazing of the liner. Glazed
liners can compromise the retention of lubricating oil,
leading to improper lubrication and increased wear.
● If mirror polishing appears, the liner has to be honed using
a honing tool.
94

Honing Procedure:
● A honing tool is a type of rubber ball tree, i.e., at the end of
several branches, rubber balls are attached.
● For honing the liner, the liner is kept in an upright position,
and the honing tool is attached to a drilling machine at the
end.
● As the drilling machine starts, the complete rubber ball tree
(honing tool) rotates and is inserted inside the bore of the
liner from top to bottom and then in reverse order to take
out the tool from the top.
● This procedure is repeated 1 or 2 times, which makes the
liner surface slightly rough to hold the lubricating oil and
avoid mirror polishing.
● After honing, clean the liner thoroughly with lint-free cloths
and diesel oil to remove all debris and rubber residues.
95

● Perform a final inspection of the liner surface under proper
lighting to ensure uniform roughness and the absence of
debris.
Jacket Frame
● Clean the jacket area thoroughly to remove deposited mud
or signs of corrosion. Use wire brushes or power tools for
stubborn deposits but ensure no damage is caused to the
frame.
● Check for any cracks or damages on the jacket frame.
Inspect corners and welds carefully, as these areas are
prone to stress-related cracks.
● Check for loose cylinder head studs. Verify torque values
against the manufacturer’s specifications using a calibrated
torque wrench. Tighten or replace studs as necessary.
● Check the condition of the boost air space for fretting or
corrosion. Inspect for oil or water leaks that might indicate
sealing issues or gasket failure.
● Clean and inspect the cooling water passages to ensure
there is no blockage due to scale or deposits. Clear
obstructions using suitable descaling agents if required.
● Examine mounting surfaces and gasket grooves for flatness
and smoothness to ensure a proper seal upon reassembly.
Connecting Rod
● Check connecting rod for any scoring or damage.
● Inspect the connecting rod bore for signs of ovality or wear,
which could impact its proper alignment with the crank pin.
96

● Ensure the oil passageways in the connecting rod are clear
of obstructions, as blockages can lead to inadequate
lubrication.
● Check for bend in the connecting rod—if there is a slight
bend, it will not be visible by eye.
● Take a brass rod or drill of such a diameter that it can go
inside the oil hole.
● If the rod is bent, the bar or drill will not travel completely
inside the bore and will get stuck at the bent point.
● If a bend is detected, measure the degree of misalignment
using a straightness gauge or an alignment jig, and replace
the rod if it is beyond allowable limits.
DP Test for Big End Halves
● Check big end halves for any cracks by doing a dye
penetrant crack test for minor cracks.
97

● Ensure proper cleaning and drying of the big end halves
before performing the DP test to ensure accurate results.
● Mark any identiﬁed cracks for further evaluation, and
consult the manufacturer's guidelines to determine if
repairs or replacements are necessary.
Con Rod’s Tie and Hydraulic Bolts
● Check tie bolt/hydraulic bolt length and compare it with the
value given by the maker.
● Check for any scoring marks, damage, cracks, etc.
● Perform dye penetrant test on the tie/hydraulic bolt to
check cracks.
● Hit the tie/hydraulic bolt with a spanner and check for a
ringing sound.
● Check the condition of threads for any damage.
98

● Replace the bolts if the running hours are completed, even
if the bolt seems normal.
● Ensure the hydraulic bolt tightening torque is in compliance
with the maker’s instructions.
● Inspect the bolt head and shank area for signs of fatigue or
plastic deformation.
● When replacing tie or hydraulic bolts, always use genuine
spares from the equipment manufacturer to ensure
compatibility and durability.
Checks on Crank Pin
● Check for any scoring or damage.
● Check for the shining of the crankpin.
● Check for any abnormal contact of the pin with the piston
and con-rod.
● Check for taper of the pin by measuring its diameter with
an outside micrometer.
● Inspect the crankpin ﬁllets for any stress concentration
marks or fatigue cracks.
● Polish minor scoring marks on the crankpin surface with
emery cloth, but consult the manufacturer before
undertaking any signiﬁcant machining or reconditioning.
Bearing Shell
Once the bearing shells are out, it is important to inspect them
before deciding to reuse them.
One must replace the bearing shells if the following inspection
shows wear out of limit as prescribed in the manual:
99

● Check for wiped-off white metal from mid, corner, or side
areas of the shell metal in the oil flow area.
● Inspect the oil grooves for any signs of blockage or uneven
wear, as this can lead to inadequate lubrication and further
damage.
● Check for discoloration, which might indicate overheating
or insufficient lubrication during operation.
● Examine the edges of the shell for burrs, sharp edges, or
deformation that may have occurred during installation or
removal.
● Ensure that the back of the bearing shell is free of dirt,
corrosion, or scratches, as these can prevent proper
seating and alignment.
● After replacement, ensure proper alignment and clearance
according to the manufacturer's manual. Incorrect
installation can lead to premature bearing failure.
100

Air Cooler Maintenance
● Clean the air cooler and its element in water mixed with a
chemical (Air cooler cleaner).
● A hot pipe of steam or heated circulating water will result in
the efficient cleaning of the element.
● Ensure the chemical cleaner used is compatible with the
cooler material to avoid corrosion or degradation.
● After cleaning, rinse thoroughly with clean water to ensure
no chemical residue is left, as this can lead to
contamination during operation.
● Check for pitting, flaking, or removal of white metal from
the shell.
● Inspect the cooler for any signs of corrosion or cracks in
the housing, which can lead to reduced cooling efficiency
or leaks.
● Examine the gasket surfaces for wear or deformation.
Replace any gaskets that show signs of deterioration to
ensure a proper seal.
● Verify the airflow through the cooler after cleaning.
Blockages or residual dirt can affect the engine's
performance.
Safety Tip: When handling chemicals or hot water during
cleaning, wear appropriate personal protective equipment (PPE),
101

including gloves, goggles, and aprons, to prevent accidents or
injuries.
102

Chapter Six
Measurement and Calibration
Measurements and Calibrations for Generator Components
After all the checks and cleaning have been performed on
various parts of the generator, it is essential to take the
measurements of components or calibrate various clearances
and dimensions to ensure that all the values are within the limits
as prescribed by the maker.
If not, the concerned part must be replaced with new spares.
Please check the gauging sheets of generator parts provided
with this eBook.
103

Cylinder Head
Valve stem and valve guide clearance:
If the clearance between the valve stem and guide increases,
exhaust can leak out from the cylinder, or the valve itself can
break. Measure the valve stem with an outside vernier caliper
and the valve guide with an inside vernier caliper.
The diﬀerence between the two values gives the clearance
value.
● Measure valve and seat angles.
● Measure the contact dimensions of the valve seat, and if it
is oﬀ-limit, replace the seat.
104

● Valve spring tension: Measure the spring's compressed
length under a specified load using a spring compression
tester. Replace the spring if the length exceeds the
manufacturer's specified tolerance.
● Inspect for surface pitting or damage on the valve and
guide, and ensure no deformation on the head mating
surface. Check the cylinder head for cracks or any
distortion using dye penetrant testing.
Piston
● Measure the diameter of the piston: Measure it at three
different parts by outside micrometer and compare the
values with the rated ones provided in the manual.
105

● Piston ring grooves: If the piston groove value increases, it
will lead to fluttering of the ring inside the groove, resulting
in ring breakage. This is to be measured with an inside
vernier caliper to determine the groove's height and depth.
● Radial Clearance: The radial clearance is the difference
between the groove depth and ring width, which can be
measured with a vernier caliper.
● Axial Clearance: It is the axial clearance between the ring
and the groove. Measure this with a feeler gauge. This
clearance is to be measured at four different points for
each ring.
106

● Butt Clearance: It is the clearance between the end butt of
the ring inside the liner. The ring is placed inside the liner,
and the impression can be taken on paper by applying
Prussian blue paste at the butt ends. The gap between the
impressions can then be measured.
Piston Pin and Piston Bore
● The connecting rod is attached to the piston by means of a
piston pin/gudgeon pin ﬁtted in the piston bore.
● Gudgeon pin dimensions: Measure using an outside
micrometer at 2-3 places, both in port-starboard and
top-bottom directions.
107

● Piston bore dimensions: Measure using an inside
micrometer at 2-3 places, as done for the pin.
● Inspect the gudgeon pin surface for wear, scoring, or
tapering. Ensure the pin bore does not have ovality, as this
can lead to improper fit and movement during operation.
Connecting Rod Big End Ovality
● For connecting rods with two pieces (oblique cut), first
tighten the bottom shell hydraulic bolts at its rated
tightening pressure.
● Hold the con-rod in the vice so that the big end is in a
horizontal position. Ensure the inner surface is properly
cleaned for measurement.
● Use a lint-free cloth to clean the surface to avoid leaving
any fibers or residue that could interfere with accurate
measurement.
● Measure the big end ovality by means of an inside
micrometer at six different positions.
● Record the measurements carefully and compare them with
the manufacturer's specified tolerances. This will help
108

identify any excessive wear or deformation that may require
corrective action.
● Ensure you rotate the micrometer slowly to get precise
readings.
● For connecting rods with three pieces, the big end part can
be separately tightened, and the same procedure as above
is to be applied.
● Additionally, check the seating surface for any irregularities
or damages before reassembly.
● Apply a light coating of machine oil to prevent rust and
ensure smooth operation.
Crank Pin Measurement
● The crank pin is to be measured by an outside micrometer
at two diﬀerent positions.
109

● Handle the micrometer carefully so as not to scratch the pin
with it.
● At each position, the pin dimension is to be measured at
port-starboard and top-bottom parts.
● It is recommended to measure in a consistent sequence,
such as starting from the top-bottom, followed by
port-starboard, to avoid missing any positions.
● After measuring, inspect the crank pin surface visually for
scoring, pitting, or any other defects. If such defects are
found, they should be documented, and appropriate
repairs, such as polishing or grinding, must be carried out.
Bearing Clearance
Main Bearing Clearance:
● When the main bearing keep is removed, insert a lead wire
of 0.5 mm thickness in between the shell and crankshaft
journal.
● Tighten the keep at its rated hydraulic pressure and then
reopen to draw out the lead wire.
● Measure the thickness of the lead wire to get the
clearance.
● It is essential to ensure that the lead wire is placed at
multiple positions along the bearing surface to account for
any uneven wear or deformation.
● Additionally, ensure that the crankshaft journal and bearing
shell are clean and free of oil or debris to avoid incorrect
readings.
110

Crank Pin Bearing Clearance:
● For crank pin bearing clearance, measure the inner
dimension of big-end housing “D,” the thickness of bearing
shells “S,” and piston pin diameter “P.”
● By calculating with these three units, crank pin bearing
clearance can be found out.
● Crank Pin Bearing Clearance Formula:
Crank pin bearing clearance = D – P – S (mm).
● Ensure that measurements of "D," "P," and "S" are taken with
precision instruments like micrometers or bore gauges and
recorded for future maintenance.
● Any deviations from manufacturer-recommended
tolerances should be addressed immediately.
Unconventional Method:
Crank pin bearing clearance can be measured at the bottom part
of the bearing by means of a feeler gauge. While using this
method, ensure the engine is in a stationary position with the
crankshaft adequately supported to prevent movement. Insert
the feeler gauge carefully to avoid damage to the bearing
surface. This method is typically used as a quick check during
routine inspections.
Thrust Bearing:
● For measuring the thrust clearance, put a dial gauge
magnet attached to the engine frame with the dial touching
the crankshaft web.
● With the help of a bar inserted in the crank web, shift the
crankshaft axially forward and measure the dial gauge
111

reading. Now shift the crankshaft axially aft again and
measure the reading, which will indicate the thrust
clearance.
● Remember not to put the bar in between the counterweight
instead of the web.
● Ensure that the dial gauge is securely mounted and
calibrated before taking readings.
● The axial movement of the crankshaft should be performed
slowly and steadily to avoid abrupt movements that might
affect accuracy.
● Compare the measured thrust clearance with the
manufacturer's specified limits to confirm the bearing's
condition.
● Excessive thrust clearance could indicate wear or
misalignment that must be addressed promptly.
Liner Calibration
Cylinder liner has to be gauged at regular intervals as specified
in the maintenance manual. The records of gauging are kept for
each cylinder, and the wear rate is calculated.
Generally, while taking the measurement, the temperature of the
liner and micrometer should be kept at the same temperature.
If the temperature exceeds that of the liner or vice versa, then
the readings have to be corrected by multiplying the value with
the correction factor and deducting the value obtained from the
reading taken.
112

The cylinder liner wear is measured by a standard template,
which consists of strategically positioned holes, wherein the
micrometer is placed and the readings are taken.
The reading obtained at the end will be the correct readings.
The readings are taken for both port-starboard and forward-aft
positions. This is done because the wear is not the same in both
directions, and the ovality is to be checked.
The wear rate will be diﬀerent across the liner. The wear will be
more in the top one-third part as combustion takes place there,
and temperatures and pressures are also very high at the top.
113

An approximate normal wear rate of the liner is about 0.1 mm per
1000 running hours.
The wear rate increases if the engine is overloaded. Generally,
the liner has to be replaced when the wear is about 0.6–0.8% of
the bore diameter or as per the manufacturer’s recommendation.
When performing liner calibration, ensure that the crankcase
environment is free from oil mist or vapor that may affect visibility
or contaminate tools and measurements.
Before gauging, inspect the liner for visible scoring, pitting, or
cracks. Such damage may affect measurements and indicates
the need for immediate action beyond wear calibration.
The calibration tools, such as templates and micrometers, should
be inspected for accuracy and recalibrated periodically as per
standard operating procedures. Using improperly calibrated
tools can lead to incorrect measurements and maintenance
errors.
After taking readings, analyze trends in the wear rate across all
liners in the engine. A uniform wear pattern indicates balanced
operating conditions, whereas uneven wear could signal issues
like improper fuel injection, cooling water flow, or cylinder
lubrication.
Addressing these issues promptly helps extend liner life and
maintain engine efficiency.
114

Shell Thickness Measurement
The bearing shell removed from the connecting rod or the main
bearing is to be measured with the help of a vernier caliper at
three points, both forward and aft.
If the diﬀerence between the two-point values exceeds 0.4 to
0.5 mm, replace both the shells.
When measuring shell thickness, ensure the vernier caliper is
free of dirt, oil, and debris. Before using, check the calibration of
the tool against a certiﬁed standard block to ensure accuracy.
115

The measurement should be taken in a clean and stable
environment to avoid ﬂuctuations caused by vibrations or
temperature changes.
Additionally, inspect the shell surface for scoring, overheating
marks, or pitting. These defects may indicate problems with
lubrication, engine alignment, or improper assembly of
components.
After completing the measurements, clean the shells thoroughly
and store them appropriately if they are reusable. Damaged or
worn shells should be tagged and documented for disposal to
prevent accidental reuse.
Also, consider performing a crankpin and main journal
calibration alongside shell measurements to ensure proper
alignment and bearing support.
Finally, document all measurements and observations in the
engine maintenance log. This record helps track component
wear over time, facilitating preventive maintenance and reducing
the risk of unexpected failures.
Gear Backlash
Backlash of gears to be measured by means of a lead wire.
Place a lead wire of 0.5 mm diameter in between two mating
surfaces of the gears. Apply grease so that the wire does not slip
out of the surface.
116

Turn the crankshaft so the lead wire gets trapped in between the
gear. Once the wire is completely compressed till the end, turn
the crankshaft in the opposite direction and take out the lead
wire.
Measure the thickness of the thinnest point in the wire which is
collapsed by both the tooth surfaces of the gear and record it as
“X” and “Y.” The backlash will be the addition of the two, i.e., “X”
+ “Y.”
Ensure that the gear housing and surrounding components are
clean and free from grease or dirt that might interfere with
accurate measurement. Inspect the compressed lead wire for
consistency across its length, as irregular thickness could
indicate uneven gear wear.
Additionally, check for noise or vibration during the gear rotation
process to identify possible misalignment or defects in the gear
teeth. Such issues, if left unchecked, may lead to excessive wear
or operational ineﬃciency.
Tappet Clearance
Tappet clearance is the distance between the valve stem top
and the rocker arm tappet.
It is a very important and critical clearance responsible for the
optimal performance of the engine because, with a change in
temperature, the valve stem also expands and contracts.
117

If the distance between the stem and the tappet increases, a
banging sound will occur, which may result in the breaking of the
valve stem or rocker area.
The value of tappet clearance varies from maker to maker. The
average value is generally 0.5 mm between the tappet and
T-yoke, measured by means of a feeler gauge.
First, the concerned unit piston is brought to TDC and in the
ﬁring position where the pushrods of both inlet and exhaust
valves are oﬀ-cam. Then clearance between the T-yoke and
valve stem is removed, i.e., made “0.”
The clearance between the T-yoke and rocker arm tappet is
adjusted to approx. 0.5 mm by loosening or tightening the
tappet adjusting screw on top of the rocker arm.
118

Before adjustment, ensure that the feeler gauge used is
calibrated and free from dirt to prevent inaccurate readings.
While loosening or tightening the tappet adjusting screw, ensure
incremental changes are made and verify the clearance
repeatedly to avoid over-tightening or loosening.
After the tappet clearance is set, rotate the crankshaft to ensure
smooth movement and recheck the clearance to confirm that it
remains consistent across multiple rotations. An inconsistent
tappet clearance could indicate worn rocker arms or misaligned
pushrods that need further inspection or replacement.
Lastly, record the tappet clearance values for each cylinder and
compare them with the manufacturer’s recommendations to
ensure compliance. Regular monitoring of tappet clearance can
help identify early signs of wear or damage in valve train
components.
Crankshaft Deflection
Crankshaft deflection must be taken twice—before starting the
decarbonization (d'carb) and after completion of d'carb. This is
done to ascertain whether the crankshaft journal is deviated
from the theoretical axis or not.
The deflection is recorded by using a dial deflection gauge,
which is fitted between the webs of the crankshaft in each unit.
The complete shaft is then rotated in the direction of the
operational rotation of the generator, which may be clockwise or
anti-clockwise.
119

The reading of the dial gauge is noted while turning the
crankshaft, which indicates the opening and closing of the webs.
Smaller readings indicate better crankshaft alignment and lower
deﬂection, ensuring the shaft operates closer to its design
tolerances.
Procedure
● With the running gear in place, the crank to be measured
has to be turned towards (before or after) B.D.C until the
120

dial gauge can be fitted next to the connecting rod at the
position indicated.
● Pre-tension the dial gauge slightly and set it to “0”.
● Turn the crankshaft with the turning gear, and record the
dial gauge reading in the crank positions as shown in the
figure.
● The difference between the indicated values at B.D.C. and
T.D.C. shows the amount of crank deflection during one
revolution.
● When measured values lie above the maximum permissible
limits, the cause has to be found, and the necessary
remedial measures taken (defective main bearing, engine
support altered due to hull deformation, loose
holding-down bolts, defective shaft line bearings, etc.).
Important Considerations
● Ensure that the environment is stable and free from
vibrations during the deflection measurement process, as
external disturbances can lead to incorrect readings.
● Take readings at consistent crankshaft positions (e.g., BDC,
TDC, and 90° intervals) to ensure accurate comparisons
across units.
● Always compare the measured deflection with the engine
manufacturer’s specifications to identify whether the values
are within permissible limits. Exceeding these limits can
cause abnormal vibrations, uneven wear, or catastrophic
failure of the crankshaft.
● If deflection exceeds limits, investigate further to identify
potential causes such as a worn-out bearing shell, improper
alignment during installation, or uneven load distribution
due to excessive thermal expansion.
121

● Document the measured values and trends over time to
track gradual deviations, which can provide early warning
of potential issues.
Remedial Actions
● If main bearings are found defective, inspect and replace
them with approved spares, ensuring proper clearance and
alignment.
● In cases of hull deformation altering engine supports,
consult with shipyard engineers to realign the foundation
and restore the structural integrity of the engine bed.
● Check holding-down bolts for proper torque and tightness.
Loose bolts can cause uneven load distribution and
crankshaft misalignment.
122

● Inspect the shaft line bearings for wear, proper lubrication,
and any signs of misalignment due to thermal stress or
external damage.
● Corrective measures, such as realignment or replacement,
should be carried out promptly.
123

Chapter Seven
Closing and Assembling
Assembling the overhauled parts of the generator requires both
accuracy and correct skills to ensure a trouble-free operation
when the engine is restarted. The sequence is in reverse order
of opening, starting with crankshaft parts, i.e., main bearing and
crank pin bearing.
Main Bearing
If the main bearing is opened up for renewal or inspection, it is to
be assembled first. Cleaning the pin surface is of utmost
importance as any foreign particle may lead to scratching of the
shell and pin.
Depending upon the type of crankshaft (underslung or regular
supported), the top or bottom shell is inserted. The same “T” tool
can be used to insert the shell with the rotation of the crankshaft.
Apply clean lube oil to the pin surface and bearing shells to
ensure smooth fitting.
Fit the shell in the correct position, as described in the manual,
into the keep of the shell. With the help of the keep fitting tool,
lift the keep into its position and insert the holding nuts. Tighten
the nuts, both keep-securing and side bolts, with hydraulic jacks
at its rated pressure given in the manual.
124

Ensure the bolts are tightened in a sequential pattern as
recommended in the manual to avoid misalignment of the
bearing.
After tightening, double-check the clearances using feeler
gauges or plastigauge to ensure they are within the specified
limits. Document these measurements for future reference.
Liner
If the liner is removed, ensure that the jacket is de-mucked from
mud deposits. Renew all the O-rings of the liner.
Lift the liner with its lifting/insertion tool, and once the liner is in
position for insertion, apply some soft soap solution to the
O-rings of the liner for smooth insertion. Take care to put the
liner in the correct direction.
Marking is provided on the liner body and the generator frames;
hence, both these markings are to be matched while the liner is
fitted back.
Before inserting the liner, inspect the bore of the liner seat for
signs of corrosion or pitting. If present, polish the bore with an
emery cloth and clean it thoroughly.
Check the concentricity of the liner seat and ensure the surface
is flush to avoid any misfit. Conduct a hydrostatic test on the
jacket if possible, to confirm the integrity of the O-rings after
installation.
125

Piston and Connecting Rod
Once all the checks and tests are performed on the piston and
connecting rod, they should be assembled back. Clean the
piston pin and piston bore, and apply lube oil at all the mating
surfaces.
On a plank of wood with the piston held vertically, insert the
connecting rod with the help of a chain block or strong wire
sling. Make sure the con-rod is inserted on the correct side by
checking the stamping marks, as the oil holes of the rod should
come in the correct position for eﬀective lubrication.
126

As the small end bore of the connecting rod matches with the
piston pin bore, insert the pin, and if required, use a mallet to
hammer the pin.
When it is ensured that the assembly is correct, with the help of
a circlip plier, insert the locking circlip over the pin. After
completing the assembly of the piston and con-rod, lift and keep
the piston in the stand.
Clean the ring groove with compressed air and prepare to insert
the ring. If a ring expander tool is provided, insert all the rings,
starting from the bottom ring (oil ring with spring coil). Make sure
the oil spring joint for the last ring is in the opposite direction of
the ring butt.
127

Ensure proper staggering of the piston ring gaps (generally 120
degrees apart) to prevent blow-by during operation. Before
inserting the piston into the liner, double-check that all piston
rings are correctly seated and are free to rotate in their
respective grooves. Lubricate the piston rings and the inner liner
surface generously with clean lube oil.
While inserting the piston into the liner, use a ring compressor
tool to compress the piston rings securely. Align the con-rod
small end with the crankpin and lower the assembly carefully to
avoid scoring or damaging the liner. After the piston is in place,
rotate the crankshaft manually to check for smooth movement
and proper alignment of all parts.
Finally, torque all connecting rod bolts to the specified values in
the manual, and perform a re-torque check after initial engine
trials to confirm no loosening has occurred during the startup
process.
Crank Pin Bearing
Depending upon the type of the connecting rod, the shell is
either fitted in the connecting rod bottom half and the
connecting rod itself (oblique cut two-piece type) or in the
128

crankpin keeps (three-piece type). Cleaning is by far the most
important point before fitting bearing shells.
Ensure that no foreign particles are present either on the pin or
in the shells. Any debris, no matter how small, can lead to
uneven load distribution and premature bearing failure. Use a
lint-free cloth for cleaning, and consider using a compressed air
blower for hard-to-reach areas.
Two-Piece Oblique Cut Con-Rod
Apply clean lube oil to the crank pin and bearing shells. Turn the
crankshaft so that the pin is in the appropriate position to fit the
bearing shells. Fit the shell in the bottom half of the keep in the
correct position.
Take the load of the bottom half with the help of a strong wire
rope or wooden plank resting on both sides of the crankcase
door for support.
Ensure that the supporting structure is stable and aligned
correctly to avoid damaging the crankcase edges or the bearing
shell during installation.
For two-piece con-rods, the complete piston is inserted along
with the con-rod fitted with the upper shell. (If the liner of that
unit is removed, it is required to fit the liner first).
Please check what points to ensure before inserting the piston in
our next section, “Piston.” Tie a piece of cloth so that the bearing
129

shell is properly held while transferring the piston-con rod
assembly into the generator for fitting.
Once the bottom shell is held in place and the piston is inserted
into the position, remove the tied cloth and slowly lower the
piston-con rod over the crank pin.
Fit the bottom half and secure both pieces together with the
bottom stud and nuts. Before tightening, ensure that the mating
surfaces are aligned, and there is no visible gap between the
shells and the crank pin. Any misalignment can result in uneven
pressure during operation.
Tighten the nut using a hydraulic jack at the rated pressure
described in the manual. After tightening, double-check the
torque values to ensure they are within the recommended
range. Conduct a final inspection to verify that no tools or foreign
objects are left inside the crankcase.
Three-Piece Straight Cut Con-Rod
For three-piece straight con-rods, the crankpin shell keep is in
two pieces without the con-rod. After cleaning thoroughly both
the pin and the shell, apply clean lube oil on the pin and shells.
Ensure the lubrication oil used is free of contaminants and
matches the manufacturer's recommended grade to avoid
compatibility issues.
First, put the bottom half of the two-piece keep with the help of a
strong rope/chain block or a flat log of wood for support. Once
130

the bottom half keep and shell are in position, the upper half
with the fitted shell is inserted. It is crucial to handle the shell
carefully to prevent it from slipping or misaligning during this
process.
Misaligned shells can result in uneven bearing wear and
potential crankpin damage. Care should be taken not to
drop/lose/misalign the fitted shell, and the stud bolt is fitted to
secure the two keeps together.
With hydraulic jacks, tighten the nut at the rated pressure as
stated in the manual. After the tightening process, inspect the
131

assembly to confirm that there are no gaps between the keeps,
and the shells are seated flush against the crank pin.
Additionally, rotate the crankshaft manually to check for smooth
movement and ensure there is no resistance, which may indicate
improper fitting or misalignment.
Additional Best Practices:
● When using hydraulic jacks, always check the condition of
the seals and hoses to avoid leakage or sudden pressure
loss during operation.
● Document the torque and hydraulic pressure values used
for reference during future maintenance cycles. This helps
maintain consistency and ensures compliance with
maintenance procedures.
● Conduct post-assembly checks, such as verifying oil flow
through the bearing, to ensure proper lubrication.
Piston
Before inserting the piston, ensure that:
● Liner is cleaned
● All calibration linked with liner and piston are taken
● Piston rings are staggered so that the butt end of any two
rings does not coincide with each other
● Piston inserting tool is placed and secured on top of the
liner
● Liner itself is secured with a liner holding tool as, in the
event of piston stuck up, the liner should not draw out
accidentally
132

● Apply lube oil for smooth insertion both in piston rings and
liner
● Gudgeon/piston pin is properly secured by circlip
● Double-check the piston grooves for any carbon buildup or
deformation, which may affect the piston ring seating.
● Verify the condition of the oil scraper rings and ensure they
are in good condition to avoid excessive oil consumption
during engine operation.
● Confirm that the liner honing pattern is intact, ensuring
proper oil retention and seating of the piston rings.
As discussed above, for a two-piece oblique-cut con-rod, the
piston is inserted while securing the crank pin bearing.
For a three-piece straight-cut con-rod, the piston is inserted after
fitting the crankpin bearing assembly.
Once the crank pin assembly is secured, all the above points are
to be taken care of before inserting the piston. Also, turn the
crankshaft so that the crank pin and the web are in the BDC
position.
Insert the piston slowly with the help of a chain block. Once the
piston reaches its seat over the crank pin shell top keep, ensure
that the surface is clean and free of oil.
Sit the piston over its matching holes and insert the tie bolts
(normally four in number) to secure the piston con-rod assembly
with the crank pin shell keep assembly.
133

Tighten the tie bolts in a cross sequence as per the rated torque
or hydraulic pressure. If new tie bolts are used, remember to
tighten all the bolts in the correct sequence and loosen them up
again.
This procedure is to be repeated 2 to 3 times to ensure that the
new tie bolts are properly elongated. Ensure to do wire lashing
of tie bolts for all the units.
Perform a ﬁnal inspection to conﬁrm that the tie bolts are evenly
torqued or hydraulically tightened to avoid uneven stress on the
crank pin assembly.
134

Recheck the piston position to ensure it is properly aligned with
the liner and there is no binding during manual rotation of the
crankshaft.
Apply a thin coat of protective lubricant to the liner and piston
skirt to prevent scoring during initial startup after assembly.
Log the torque values and sequence in the maintenance records
for reference during future inspections or overhauls.
Cylinder Head
Fit piston cleaning ring/fire ring/protecting ring inside the liner
before fitting the head and ensure that all the cylinder head
mountings are completed, including:
● Cleaning and inspecting the liner top thoroughly for any
residual carbon or deposits to ensure a proper seal. Pay
special attention to the condition of the fire ring seat.
● Check the liner wall for scratches, scoring, or wear, as it can
directly affect engine performance. Rectify any issues
before proceeding.
Start Air Valve
It has to be fitted with new O-rings and washers. Ensure the
valve is pressure tested and the seating surface is smooth and
free from damage.
135

Indicator Cock and Relief Valves
Tested indicator cock and relief valves to be fitted with new
washers. Ensure both are functioning smoothly and the threads
are free of dirt or oil residues.
Valve Seat to be Fitted if Renewed
For fitting the valve seat, first cool down the seat in liquid
nitrogen, which will shrink its size. Renew the O-ring for the valve
seat and, with the help of a seat fitting tool, push the seat into
place.
Ensure the cooling process is performed in a safe environment
to avoid handling hazards. Wear appropriate safety gear.
If a tool is not provided, use the old valve, which will act as a tool
to fit the seat. After fitting, inspect the valve seat with a flashlight
or borescope to confirm proper alignment and seating.
136

Valves with Spring and Roto Caps:
Fit the valves with their springs, roto caps, and original cotters.
Ensure the springs are tensioned correctly.
Fit Plugs and Temperature Gauge: Carefully tighten all plugs and
install the temperature gauge. Verify the gauge calibration to
avoid inaccurate readings during operation.
Fuel Injector:
Pressure-tested injectors are to be fitted with new O-rings and
washers after the head is fitted on the generator frame.
Before installation, visually inspect the injectors for any signs of
damage or clogs and clean the nozzle tip thoroughly if required.
Before fitting the head, test all the roto-caps over the valves to
ensure they are working properly by hitting the upper portion of
the valve with a mallet. Once the valve is hit, the roto-cap will
rotate and stop, ensuring proper functionality.
Once all the head fittings are completed, the cylinder head is to
be lifted with its lifting tool and the chain block over the
generator frame.
Inspect the lifting tool for any wear or damage to avoid accidents
during the lift. Ensure to apply Molycote (Hi-temperature
anti-seize compound) in the exhaust side joints and bolts,
injector seating area, etc.
137

Once the head is ready to fit, apply silicon to the water O-rings.
Make sure all O-rings (water side and lube oil sides) are fitted
properly.
Put the cylinder head gasket on top of the liner and apply
Molycote. Check that the gasket is aligned correctly with no
overlap or protrusions that could lead to leaks. Slowly lower the
head onto the liner without damaging any stud or misaligning
any O-rings and gaskets. Check that the head is level over the
liner from all directions. Use a spirit level if needed to ensure
even seating.
Once everything is okay, put the nut over the studs and, with the
help of a hydraulic jack or torque wrench, tighten the head as
per the rated pressure or torque described in the maker's book.
Follow a star pattern tightening sequence to ensure uniform
pressure distribution across the head.
Remember to complete all the cylinder head connections only
after the head is tightened to its rated torque. Start with all the
water connections first, and once the water connections are
complete, open the water system and check for leaks. If no
water leakage is observed, adjust the tappet clearance of all the
unit's exhaust and inlet valves.
138

Fuel Pump and Connections
The overhauled fuel pumps to be fitted and the high-pressure
pipe connecting the pump to the injector to be fitted back.
Before connecting, ensure that the high-pressure pipe is
thoroughly inspected for cracks, wear, or pitting, as these could
lead to leakage under high pressure. Clean the pipe and
connection threads to remove any dirt or debris that could
hinder proper sealing.
Fit all the other connections such as leak-off line, return line, etc.,
which were removed before lifting the head from the frame.
Check all gaskets and seals in the connections for wear or
damage and replace them as necessary.
139

Tighten connections as per torque specifications to prevent
over-tightening or loosening under operation. Fit all the
protection shield covers such as flywheel cover, fuel pump case
area protection cover, etc. Inspect the protective covers for any
signs of deformation or damage.
Any compromised covers must be repaired or replaced to
ensure safe operation and prevent foreign objects from entering
the machinery during operation.
Isolation Rubber
If the rubber is renewed, the new rubber pad will be difficult to
go inside the slot in the flywheel. To insert the rubber:
● Turn the flywheel such that the rubber is easy to insert.
● While holding the rubber, put a wooden plank in the face of
the pad, and with a small jack, apply hydraulic pressure to
insert the pad inside the slot.
● Tighten the bolt and nut and repeat the procedure for other
pads.
Ensure that the rubber pads are the correct size and material as
per the manufacturer's specifications. Improper pads could result
in improper damping and excessive vibrations during operation.
Clean the slot in the flywheel thoroughly before inserting the
pad to remove any accumulated dirt, grease, or rust, which could
prevent proper seating of the rubber.
Once all the rubber pads are fitted, manually rotate the flywheel
to confirm uniform clearance and proper alignment of the pads.
140

Check for any abnormalities such as wobbling or unusual
resistance. Document the replacement process, including the
batch numbers of the new rubber pads, for maintenance
records.
Safety Tip: While handling hydraulic jacks and wooden planks,
ensure that all tools are in good condition and used correctly to
avoid injuries or damage to components. Use protective gloves
while ﬁtting rubber pads to prevent hand injuries.
141

Chapter Eight
Alternator Maintenance
The alternator on the ship is exposed to harsh weather and sea
conditions, due to which its capacity and eﬃciency tend to
reduce.
It is, therefore, very important to have proper maintenance on
the alternator part of the generator as per planned maintenance
or as and when it is required.
Regular maintenance ensures optimal performance, prolongs the
lifespan of the alternator, and reduces the risk of unexpected
failures.
142

Cleaning and checks
Before starting any maintenance work on the alternator, all
safety precautions should be taken, and the alternator should be
shut and locked down. Post notice and ply cards on relevant
places. Also, alternator heater is to be isolated.
Ensure that the power supply to the alternator is completely
disconnected and the system is de-energized to avoid
accidental starts or electrical shocks. Use proper personal
protective equipment (PPE) such as insulated gloves, safety
glasses, and ear protection as necessary.
● Clean the alternator ventilation passage and the air ﬁlter.
Ensure that any accumulated salt deposits, grease, or dirt
are carefully removed to prevent airﬂow obstruction.
143

● Inspect the alternator casing for signs of corrosion, cracks,
or physical damage. Rectify or report any such findings
immediately.
● Check the insulation resistance of the stator and rotor
windings. Record the insulation values and compare them
with previous readings to identify any trends of
degradation. If the resistance drops below acceptable
limits, consider rewinding or varnishing the windings.
● Air gap between stator and rotor to be checked and
maintained between 1.5 to 2 mm. Use a feeler gauge to
measure the air gap at multiple points around the
circumference to ensure uniformity. An uneven air gap can
lead to vibration and reduced efficiency.
● Slip rings to be checked for wear down and must be
renewed if required. Polish slip rings gently with fine emery
paper to remove minor oxidation or scoring. Ensure a
smooth surface finish to maintain proper electrical contact.
● Carbon brushes to be cleaned and checked for free
movement. Replace brushes that are worn below the
manufacturer’s recommended minimum length. Also,
inspect the brush holders for any signs of corrosion or
distortion.
● The brush contacting pressure to be checked by spring
balance. Refer to the manufacturer’s manual for the correct
pressure range and adjust the springs if required. Improper
pressure can cause sparking or uneven wear on the slip
rings.
● Automatic Voltage Regulator (AVR) to be checked and
cleaned of oil and dust. Verify the proper functioning of the
AVR by testing its output voltage against setpoints. Replace
144

any faulty components to ensure voltage stability during
operation.
● Alternator sensors to be cleaned. Inspect the sensors for
proper alignment and functionality. Faulty sensors can lead
to inaccurate readings, affecting system performance.
● Check all electrical connections for tightness and signs of
overheating or arcing. Loose or corroded connections can
lead to voltage drops or electrical failures. Tighten or
replace them as necessary.
● Inspect the bearings for any signs of wear or damage.
Lubricate the bearings as per the manufacturer's
recommendations to ensure smooth rotation. If noise or
vibration is detected during operation, consider replacing
the bearings.
● Examine the alternator coupling for proper alignment with
the prime mover. Misalignment can cause vibration, reduce
efficiency, and lead to premature wear of components.
Correct any misalignment immediately.
● Inspect the diode assembly for any signs of damage or
malfunction. Replace any damaged diodes to ensure
consistent rectification of the AC output.
Maintenance
● A vacuum cleaner can be used to remove dust
accumulated in the inner parts of the alternator.
● The terminal box cover gasket to be checked for proper oil
and water tightness.
● All the connections in the terminal box to be tightened
properly.
● Cable gland to be checked for integrity.
145

● Forced ventilation around the alternator must be
maintained at all times.
● Check heater for proper operation.
● Check and do contactor routine of Air Circuit Breaker (ACB)
at the Main Switch Board (MSB).
● The foundation bolts of the alternator to be checked for
tightness.
146

Maintain a detailed log of maintenance activities, including
observations, tests performed, and any parts replaced, to ensure
proper tracking of the alternator’s performance and history.
147

Chapter Nine
Starting Preperation
After thorough inspection of all the assembled parts, the
generator is prepared for starting. If working in a team, ensure to
give proper signaling signs before starting the engine, even if it
is for a short duration.
Ensure no one is nearby the crankcase door or on top of the
engine when starting. But for starting the generator, all the
isolated systems are to be brought to normal condition ﬁrst.
Starting with:
Water System
● Check all the connections are proper and tight
● Close the water drain valve
● Open vent provided in the jacket water outlet for air
purging
● Open the line valve for water coming from the expansion
tank
● Keep an eye on any leakages from cylinder head
connections and liner/head surface where water O-rings
are placed
● Keep checking for water from the vent
● If you ﬁnd any leakages, shut the expansion line valve and
drain the water to rectify the leakage
● Ensure all trapped air is purged, and once water comes out
from the vent, shut the vent valve
148

● After the above checks, start opening the water outlet valve
slowly, keeping an eye on the jacket water pressure of the
running machinery
● After the outlet valve is fully open, start opening the inlet
valve very slowly, as the sudden opening of the same will
ﬂuctuate the water pressure of the line (i.e., in other running
generators).
Lubricating System
Before starting the generator after a major overhaul, the sump
has to be drained of contaminated oil and cleaned thoroughly.
Check the sump for any leftover tools or rags. Take fresh charge
of lube oil till the appropriate level.
149

All the filters in the system, which include duplex lube oil filter,
turbocharger lube oil filter, and centrifuge filter, must be cleaned
before activating the lube oil system.
Following checks to be performed in the lube oil system:
● Check for any lube oil leakages, and if seen, stop the pump
and rectify the leakages
● Check the lube oil flow from the piston and con-rod
● Before starting the engine, engage turning gear and turn
the engine for at least 30 minutes with the priming pump
on
● Check the ampere of the turning gear motor
● If the current is higher than normal, there is some problem
or obstruction for the crankshaft while turning.
● Rectify the fault before starting the engine
150

● Check the ﬂow of oil over the connecting rod
Fuel System
● Ensure that all valves in the diesel oil lines are open to the
generator, including oil outlet returning to the diesel oil
service tank.
● If a booster and circulating pump are provided in the line,
ensure that all the valves of the pumping system are in the
open position and then start the pumps.
● Check all the connections are proper and tight.
● Start the lube oil priming pump and initially do the purging
through the lube oil ﬁlter vent or purging cock
● Once the oil starts coming out of the purging cock, shut the
cock
151

● Always start the booster pump ﬁrst, then the circulating
pump.
● Check pressure on local gauges located near both the
pumps and on the local panel of the generator.
Air System
● Drain the air line and the air bottle which provides starting
air to the generator
● Check all the air line connections
Slowly open the starting air valve to the generator
● If any leakage is found, shut the air valve and rectify the
leakages
● Open the indicator cock, remove or disengage the turning
gear, and blow through the engine
● To check starting air valve leakage, while the engine is
blown through, feel the leakage at every starting air valve in
each head
● Always ensure that air receivers are adequately charged
before attempting to start the engine. Low-pressure air can
hinder engine cranking.
Once all the above checks are done, the generator is ready to
start.
General Checks and Precautions
● Be sure to disengage the turning gear or remove the
tommy bar before starting the engine
152

● Check all the oil levels (i.e., in sump, pedestal bearing,
governor, and in turbocharger)
● Ensure to pre-lubricate the engine either by priming pump
or hand-driven pump
● Turn on the power supply of the engine protecting devices
● Ensure all trips are correctly set
● Ensure overspeed mechanical trip is correctly set
● Never start the engine from a remote position. Always start
it from the local side with enough manpower for
observation purposes
● If while starting, any abnormal noise occurs or the engine
picks up speed very rapidly, immediately stop the engine
and remove the cause of the trouble
153

● Ensure that tools, rags, or any loose items are completely
removed from the engine vicinity and crankcase area
before starting.
● Check for proper operation of alarms and shutdown
systems before initiating the startup process. Functional
alarm systems can prevent engine damage.
● Inspect turbocharger inlet and outlet for any blockages.
● Restricted airﬂow can lead to performance degradation.
● Before starting, conduct a ﬁnal walk-around inspection of
the generator to ensure no unauthorized personnel or
equipment is in proximity.
154

Chapter Ten
Running In
The newly ﬁtted liner, piston, or piston rings are machined
prepared in the workshop ashore. They have surface asperities,
and there is no bedding between the moving surfaces, i.e., liner
and rings. Hence thorough inspection and gradual running in is
necessary.
Under such situations, if proper step-by-step running is not
followed, then it may lead to heavy blow-past of combustion
155

gases. The blow-past can be dangerous as it can lead to
contamination of expensive crankcase lube oil and may result in
a crankcase fire.
Hence, initially, a step-running program is required for newly
fitted piston, piston rings, and liner.
After a complete d’carb of the engine, it is important to keep an
eye on various parameters of the engine under increasing load,
which can be achieved by Running In.
Running In is a program followed after overhauling, and it is a
long-run program with a step-by-step increase in the load and, in
some generators, speed of the engine (for the initial start).
The running-in schedules are provided in the engine manuals
and differ from part to part. The most general running-in
sequence is as follows:
After all the checks are complete on the generator:
● Ensure that the generator is on diesel fuel.
● Check that the turning gear is disengaged.
● Start the generator locally and ensure enough manpower is
present.
● Ensure the “auto-synchro” option is off in the ECR;
otherwise, the generator will come on load automatically.
● Run the generator for 5 minutes in no-load condition and
stop it from local.
● While the generator is running, record all parameters.
156

● After the crankcase is cooled down and safe to open,
remove all the crankcase doors and perform a crankcase
inspection.
● Check the condition of the crankcase for oil splashes, loose
particles, or metal shavings that may indicate abnormal
wear or damage.
● Inspect for abnormal noises or vibrations during operation,
as these may point to misalignments or issues in the
reciprocating parts.
● Check the temperature of the con-rod bearing.
● Check the ﬂoating of the connecting rod using a rod (try
moving the rod in the lateral direction of the pin) and oil
condition for white metal or hotspots.
157

Start the generator again for the next 10 minutes and repeat the
above inspection process.
Start and run the generator for 30 minutes on low load (25%) and
repeat the crankcase inspection. Ensure that, before opening,
the crankcase is cooled down within safe limits.
Start and run the generator for 3 hours at 25% load, and after
stopping, perform a crankcase inspection.
If the crankcase inspection until now is satisfactory, start and run
the generator for 3 hours at 50% load.
158

Keep monitoring all engine parameters, including crankcase
temperature.
Increase the load of the generator to 75% for the next 3 hours,
followed by an increase in load to 85% for 3 hours.
Finally, run the generator for 4 hours at 90-100% load, and this
time, record the Pmax by peak pressure gauge or by digital
pressure indicator to check the combustion of each cylinder.
Once the running is completed, do a thorough crankcase
inspection.
Evaluate the condition of lubricating oil in the sump for any
contamination by metal particles, carbon deposits, or water
ingress. Perform oil analysis to conﬁrm its suitability for further
use.
The generator should run on diesel for more time (at least 48
hours but depending upon the maker's instructions), and after
100 hours of running, a crankcase inspection should be
performed along with tightness checking of all the bolts (big-end
and tie bolts).
The running hour period as per increasing load may diﬀer
according to the “generator's” make. Please refer to the manual
for the proper running hour period.
159

Conclusion
Marine engineers working on different types of ships around the
world have admitted facing a variety of problems related to the
generator d'carb procedure.
Considering the fact that overhauling generators is a tedious and
complicated task that requires simultaneously carrying out a
variety of systematic procedures in a limited time frame, a
number of important aspects need to be taken care of to avoid
unnecessary mistakes and unfortunate accidents.
This guide is a result of years of experience, knowledge, and
skills, brought together to ensure a solid reference for shipping
professionals who are involved with generator overhauling
procedures.
It aims to not only serve as a technical manual but also to
emphasize safety and operational efficiency while undertaking
this crucial task.
We at Marine Insight understand that carrying out a successful
generator d'carb involves a variety of procedures, guidelines,
and tools, which may differ from ship to ship.
Different ships and manufacturers employ unique designs and
operational techniques, necessitating a tailored approach to the
overhauling process. Therefore, engineers should always
cross-check with the manufacturer's manual and ship-specific
instructions before starting the procedure.
160

Several aspects have been taken into consideration to inculcate
all the important aspects required for overhauling generators of
different types and brands.
Special emphasis has been laid on the role of teamwork and
communication among the engine room staff to ensure seamless
coordination during the d'carb process. Miscommunication can
lead to errors that might compromise safety and lead to
operational delays.
However, if you have questions or comments regarding the
generator d'carb procedure, we would love to hear about them,
along with your experiences and knowledge. Please feel free to
contact us at info@marineinsight.com.
Your feedback is valuable and can help us enhance future
editions of this guide. Sharing your challenges and solutions can
also benefit the larger maritime engineering community.
If you want to contact the author, you can connect with him on
LinkedIn: https://www.linkedin.com/in/anish-wankhede/ or mail
him at anishw@marineinsight.com.
161

Additional Resource for Engineer Oﬃcers:
eBooks : learn.marineinsight.com
Courses: academy.marineinsight.com
AI Assistant: marinegpt.marineinsight.com
162

Step by Step Guide to OVERHAULING GENERATORS on Ships

More Related Content

Similar to Step by Step Guide to OVERHAULING GENERATORS on Ships

More from Mahmoud Moghtaderi

Recently uploaded

Step by Step Guide to OVERHAULING GENERATORS on Ships