Testing For Overhaul - Westerbeke 8.0KW-60Hz 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 wom plugs or fueVcarburetor
problems .. The decrease in compression pressure is caused
by many factors. 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 wom 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 carburetor performance or worn plugs.
They are caused also by defective electrical devices such as
the battery, alternator or starter. 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 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.
When the 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 compression valves are at minimum or
below.
NOTE:
Make cenain the engines valve clearances are
properly adjusted. An incorrect valve clearance can cause
symptoms that might, incorrectly, suggest an engine
overhaul (cylinder misfire, white smoke, noise, etc).
Before preparing for an engine overhaul, adjust the valve
clearances to the correct specification. install a new cover
gasket and test the engine.
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
the 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 extemal appearance or
its performance.
• Do not remove or disassemble parts that require no
disassembly.
• Carefully inspect each parts after 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 the proper tools. Apply oil when necessary. Take
special care to keep the fuel system parts
free
from the
intrusion of dust and
dirt.
-..v: WESTERBEKE
Engines & Generators
3