Yamaha RS90K, Service Manual

Page: 76 / 841

2-17
INSP
ADJ
COMPRESSION PRESSURE MEASUREMENT
COMPRESSION PRESSURE
MEASUREMENT
NOTE:
Insufficient compression pressure will result in a
loss of performance.
1. Measure:
• Valve clearance
Out of specification
→
Adjust.
Refer to “VALVE CLEARANCE ADJUST-
MENT”.
2. Start the engine, warm it up for several minutes,
and then turn it off.
3. Remove:
• Spark plug
CAUTION:
Before removing the spark plugs, use com-
pressed air to blow away any dirt accumulated
in the spark plug wells to prevent it from falling
into the cylinders.
4. Install:
• Compression gauge
1
5. Measure:
• Compression pressure
Above the maximum pressure
→
Inspect the
cylinder head, valve surfaces, and piston
crown for carbon deposits.
Below the minimum pressure
→
Squirt a few
drops of oil into the affected cylinder and
measure again.
Refer to the following table.
Compression gauge:
90890-03081, YU-33223
Compression gauge adapter:
90890-04136, YU-33223-4
Compression pressure
(with oil applied into cylinder)
Reading Diagnosis
Higher than
without oil Piston ring(-s) wear or
damage
→
Repair.
Same as
without oil
Piston, valves, cylinder
head gasket or piston
possibly defective
→
Repair.
Compression pressure (at
sea level)
1