Testing For Engine Overhaul - Westerbeke 6.5 MCG Service 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 detennined 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 improper oil, clogged filters or a faulty
carburetor.
The decrease in compression pressure is caused by many fac-
tors. It is, therefore, necessary to detennine 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 oU consumption ·
4 Hard
engine starting
5 Noisy engine operation
These symptoms often appear together. Symptoms 2 and 4
can result also from improper fuel regulation or a faulty car-
buretor. They are caused also by defective electrical devices
such as the battery, starter or spark 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 combus-
tion is obtained only under sufficient compression pressure.
·If
an engine
lacks
compression pressure, incomplete combus-
tion of fuel will take place even if other parts of the engine
are operating properly. To detennine the period of engine
overhaul, it is important to measure the engine compression
pressure regularly. At the same time, the engine speed at
which the measurement 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:
To test engine co~ression see the ENGINE
ADJUSTMENT section of this manual.
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,
blow by evident,. and
comp~ssion val~es
are at n:Unimurn or
below. Refer to the following page for testing engine compression.
2
ENGINE OVERHAUL
The following sections contain detailed information
relating to the major components and systems of the engine.
Included are disassembly and inspection instructions for the
guidance of suitable equipped and staffed marine engine ser-
vice and rebuilding facilities. The necessary procedures
should be undertaken only .by such facilities.
Additional detailed information and specifications are
provided in other sections of this manual, covering the
generator, alternator, starter motor, engine adjustments,
cooling pumps, etc.
DISASSEMBLY
1. Before disassembly and cleaning, carefully check for
defects which eannot be found after disassembly and
cleaning. '
2. Clean the engine exterior. ·
3. Perform disassembly in a proper order using proper tools.
Keep disassembled parts in order. Apply oil when neces-
sary. Take special care
to
keep the fuel system parts from ·
intrusion of dust and
dirt
The generator serial
number
is
stamped
· on the top the
generator
nu1~;su1g
••
PCINTERFACESOFnNARE
The engine serial
number is stamped
\ into the engine block.
.~
'
Prior to overhaul, it is advised to operate the unit with PC
Interface Software connected to the ECU. This will help
determine system operation and whether system components
may need ~placement during overhaul. .