Yamaha 2004 YXR660 Service Manual page 85

MEASURING THE COMPRESSION PRESSURE
5. Remove:
• spark plug
6. Attach:
• adapter
• compression gauge 1
Compression gauge
P/N. YU-33223, 90890-03081
Adapter
P/N. YU-33223-4, 90890-04082
7. Measure:
• compression pressure
Above the maximum pressure:
Check 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 table below.
Compression pressure
(with oil introduced into cylinder)
Reading
Higher than
without oil
Same as with-
out oil
Compression pressure
(at sea level)
Standard:
1,324 kPa
(13.24 kg/cm
Minimum:
1,150 kPa
(11.5 kg/cm
Maximum:
1,480 kPa
(14.8 kg/cm
M MMM M MMM M M MMM M
a. Crank over the engine with the electric
starter (be sure the battery is fully charged)
with the throttle wide-open until the com-
pression reading on the gauge stabilizes.
3 - 12
CHK
ADJ
Diagnosis
Worn or damaged pis-
tons
Defective ring(s), valves,
cylinder head gasket or
piston is possible.
2
, 188.31 psi)
2
, 163.57 psi)
2
, 210.50 psi)
M MMM M M MMM M M MMM M MMM