Yamaha SR125 1997, Service Manual

Page: 55 / 243

3-9
COMPRESSION PRESSURE MEASUREMENT
INSP
ADJ
NOTE:
CAUTION:
SR303060
COMPRESSION PRESSURE MEASUREMENT
Insufficient compression pressure will result in
performance loss.
1. Check:
Valve clearance
Out of specification
Adjust.
Refer to “VALVE CLEARANCE ADJUST-
MENT” section.
2. Start the engine and let it warm up for several
minutes.
3. Turn off the engine.
4. Remove:
Spark plug
Before removing the spark plug, use com-
pressed air to blow away any dirt accumu-
lated in the spark plug well to prevent it from
falling into the cylinder.
5. Attach:
Compression gauge
1
Compression gauge:
90890-03081
Adaptor:
90890-04082
6. Measure:
Compression pressure
If it exceeds the maximum pressure allowed
Inspect the cylinder head, valve surfaces
and piston crown for carbon deposits.
If it is below the minimum pressure
Squirt
a few drops of oil into the affected cylinder
and measure again.
Follow the table below.
Compression pressure p p
(With oil applied into cylinder)
Reading Diagnosis
Higher than
without oil
Worn or damaged pistons
Same as
without oil
Possible defective ring(s),
valves, cylinder head gas-
ket or piston
Repair.