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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.
111e decrease in compression pressure is caused by many fac-
tors. 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 LQw engine power output
2 Increased fuel consumption
3 Increased on 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. Thetefore.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 determine 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 engme rpm. The engine rpm can be measured at the
front end of the crankshaft.
NOTE:
To test engine compression 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.
\Vhen 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 178 psi (1260 Kpa) at
250
rpm.
With
a limit
137
psi ( 860 Kpa). Pressure should not
differ by more than 14 psi ( 100 Kpa) between cylinders. See
ENGINE
COMPRESSION in this manual.
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, startex: motorrengine. adjustments,
cooling pumps, etc.
DISASSEMBLY
1. Before disassembly and cleaning, carefully check for
. defects which cannot 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.
l"ffV'lWESTERBEKE
) Engines
&
Generators
3
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