Compression Pressure; Standard Compression Pressure - Komatsu 4D98 Series Shop Manual

2. Troubleshooting
2.2 Troubleshooting by Measuring Compression Pressure
Compression pressure drop is one of major causes of increasing blowby gas (lubricating oil
contamination or increased lubricating oil consumption as a resultant phenomenon) or starting
failure. The compression pressure is affected by the following factors:
1. Degree of clearance between piston and cylinder
2. Degree of clearance at intake/exhaust valve seat
3. Gas leak from nozzle gasket or cylinder head gasket
In other words, the pressure drops due to increased parts wear and reduced durability resulting
from long use of the engine.
A pressure drop may also be caused by scratched cylinder or piston by dust entrance from the
dirty air cleaner element or worn or broken piston ring. Measure the compression pressure to
diagnose presence of any abnormality in the engine.
(1) Compression pressure measure-
ment method
@
After warming up the engine, re-
move the fuel injection pump and
valves from the cylinder to be mea-
sured.
@ Crank the engine before installing
the compression gage adapter.
'1. Perform cranking with the regu-
lator handle at the stop position
(no injection state).
*2. See 11.2 - 18 in Chapter 11 for
the compression gage and com-
pression gage adapter.
Measurement the compression pressure
@I Install the compression gage and compression gage adapter at the cylinder to be mea-
sured.
*Never forget to install a gasket at the tip end of the adapter.
@
With the engine set to the same state as in @ '1, crank the engine by the starting motor
until the compression gage reading is stabilized.
(2) -Standard compression pressure
[Engine compression pressure list (reference value)]
Engine model
Compression pressure Mpa(kgf/cm2)
at 250 rpm
Standard Limit
Dispersion among
cylinders (kgf/cm*)
4TNE94/98/106(T) 1 3.43+0.1(35+1) / 2.75&0.1(28&l) j
0.2-0.3(2 - 3)
2-5