Testing For Overhaul; Disassembly; Assembly - Westerbeke 12C-TWO Operator's Manual

TESTING FOR OVERHAUL
HOW TO DETERMINE ENGINE OVERHAUL PERIOD
Cause of Low Compression
Generally, the time at which an engine should be overhauled
is determined by various conditions such as lowered engine
power output, decreased compression pressure, and increased
fuel and oil consumption. The lowered engine power output
is not necessarily due to trouble with the engine itself, but is
sometimes caused by injector nozzle wear or injection pump
wear. The decrease in compression pressure is caused by
many factors. It is, therefore, necessary to determine a cause
or causes on the basis of data produced by periodic
inspection and maintenance. Oil analysis on a seasonal basis
is a good means of monitoring engine internal wear. When
caused by worn cylinders or piston rings, the following
symptoms will occur:
1 Low engine power output
2 Increased fuel consumption
3 Increased oil consumption
4 Hard engine starting
5 Noisy engine operation
These symptoms often appear together. Symptoms
2
and
4
can result also from excessive fuel injection, improper injec-
tion timing, and wear of the injectors. They are caused also
by defective electrical devices such as the battery, alternator,
starter and glow plugs. Therefore it is desirable to judge the
optimum engine overhaul time by the lowered compression
pressure caused by worn cylinders and pistons plus increased
oil consumption. Satisfactory combustion is obtained only
under sufficient compression pressure. If an engine lacks
compression pressure, incomplete combustion of fuel will
take place even if other parts of the engine are operating
properly. To determine the period of engine overhaul, it is
important.to measure the engine compression pressure regu-
larly. At the same time, the engine speed at which the mea-
surement of compression pressure is made should be checked
because the compression pressure varies with engine rpm.
The engine rpm can be measured at the front end of the
crankshaft.
NOTE:
In case of severe vibrations and detonation noise, the
cause may be fu~l injector problems, see FUEL INJECTORS.
Pool fuel quality, contaminates and loss of positive fuel
pressure to the injection pump will result in injector faults.
NOTE:
Make certain the engines valve clearances are
properly adjusted. An incorrect valve clearance can cause
symptons that might, incorrectly, suggest an engine overhaul
(cylinder misfire, white smoke, noise, etc).
OVERHAUL CONDITIONS
Compression pressure tends to increase a little in a new
engine until piston rings and valve seats have been broken in.
Thereafter, it decreases gradually with the progress of wear of
these parts.
When decrease of compression pressure reaches the repair
limit, the engine must be overhauled.
The engine requires overhaul when oil consumption is high,
blowby evident, and compression values are at minimum or
below. Engine compression should be 28 kg/cm
2 ,
398 psi at
280 rpm. The maximum difference between cylinders must not
exceed 10%.
Minimum compression of 355 psi (25 kg/cm
2 )
is an indication
for overhaul.
NOTE:
For Testing Compression Pressure and Oil Pressure,
refer to the Table of Contents.
DISASSEMBLY
NOTE:
Before disassembly and cleaning, carefully check
for defects which cannot be found after disassembly and
cleaning.
• All disassembled parts should be carefully arranged in
order of reassembly. Mark or label the parts as needed
to insure proper mating and reassembly in the proper
directions and positions.
• If the disassembly procedure is complex requiring many
parts to be disassembled, the parts should be disassembled
in a way that will allow them to be efficiently reassembled
without any change in the engine's external appearance or
its performance.
• Do not remove or disassemble the parts that require no
disassembly.
• Carefully inspect each part after its removal for damage,
deformation, and other problems.
•
Carefully check gaskets, packings and oil seals, even if
checking is not specified. Replace with new ones if defective.
• Be careful not to damage the disassembled parts. Keep the
parts clean.
• Use proper tools. Apply oil when necessary. Take special
care to keep the fuel system parts free from the intrusion
of dust and dirt.
ASSEMBLY
1. Wash all parts, except for oil seals, 0-rings, rubber sheets,
etc., with cleaning solvent and dry them with pressure air.
2. Always use tools that are in good condition and be sure
you understand how to use them before performing any
job.
3. Use only good quality lubricants. Be sure to apply a coat
of oil, grease or sealant to parts as specified ..
4. Be sure to use a torque wrench to tighten parts for which
torques are specified.
Engines
&
Generators
3