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 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 inspec-
tion 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
plugs and nozzles. They are caused
also by defective electrical devices such as the battery, alter-
nator, 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 over-
haul, it is important to measure the engine compression pres-
sure 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 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.
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 valves are at minimum or
below.
Engine compression should
be
30
kg/cm2,
427
psi at
200
rpm.
Cylinder compression should not vary by
more
than
42.7 psi (3.0
kg/Cm2J.
DISASSEMBLY
1. Before disassembly and cleaning, carefully check for
defects which cannot be found after disassembly and
cleaning.
2. Drain water, fuel and oil before disassembly.
3. Clean
or
wash the engine exterior.
4.
Do
not remove or disassemble the parts that require no
disassembly.
5. 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.
6. Carefully check gaskets, packings and oil seals even
if
check-
ing is not specified. Replace with new ones
if
defective.
Engines & Generators
7