Troubleshooting By Measuring Compression Pressure; Compression Pressure Measurement Method - Yanmar 2TNV70 Service Manual

TROUBLESHOOTING
TROUBLESHOOTING BY
MEASURING COMPRESSION
PRESSURE
Compression pressure drop is one of major causes
of increasing blow-by gas (engine oil contamination
or increased engine 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
The pressure will drop due to increased parts wear.
Pressure drop reduces the durability 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 determine
the condition of the engine.
Compression Pressure Measurement
Method
1. Warm up the engine.
2. Stop the engine. Remove the high-pressure fuel
injection lines as an assembly from the engine.
See Removal of High-Pressure Fuel Injection
Lines on page 7-10. Remove the fuel injector
from the cylinder to be measured. See Removal
of Fuel Injectors on page 7-22.
Remove or install the high-pressure fuel injection
lines as an assembly whenever possible.
Disassembling the high-pressure fuel injection
lines from the retainers or bending any of the fuel
lines will make it difficult to reinstall the fuel lines.
13-4

Troubleshooting By Measuring Compression Pressure

NOTICE
3. Turn off the fuel supply valve in the fuel supply
line. Disconnect the fuel injection stop solenoid
at the connector. Crank the engine for a few
seconds with the stop solenoid disconnected
(no injection state) before installing the
compression gauge adapter (Figure 13-1, (1)),
this will expel any residual fuel from the
cylinder.
4. Install one injector gasket at the tip end of the
compression gauge adapter. Install the
compression gauge and the compression
gauge adapter at the cylinder to be measured.
5. Crank the engine until the compression gauge
reading is stabilized.
1
Figure 13-1
6. After performing the compression check,
remove the compression gauge and
compression gauge adapter from the cylinder.
Reinstall the fuel injector, high-pressure fuel
injection lines and reconnect the stop solenoid.
See Installation of the Fuel Injectors on
page 7-28 and Installation of High-Pressure
Fuel Injection Lines on page 7-11.
7. Turn on the fuel supply valve and reconnect the
injection pump stop solenoid.
8. Prime the fuel system. Check for leaks. Test the
engine.
TNV IDI Service Manual