Compression Pressure Measurement - Yamaha RS90K Service Manual

COMPRESSION PRESSURE MEASUREMENT

1
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
Compression gauge:
90890-03081, YU-33223
Compression gauge adapter:
90890-04136, YU-33223-4
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 pressure
(with oil applied into cylinder)
Reading
Higher than
without oil
Same as
without oil
2-17
INSP
ADJ
Diagnosis
Piston ring(-s) wear or
damage → Repair.
Piston, valves, cylinder
head gasket or piston
possibly defective →
Repair.
Compression pressure (at
sea level)