Yamaha YFM660FS Grizzly 4x4 Supplementary Service Manual page 172

MEASURING THE COMPRESSION PRESSURE
6.Measure:
Compression pressure
G
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 cyl-
inder and measure again.
Refer to the table below.
Compression pressure
(with oil introduced into cylinder)
Reading
Higher than
Worn or damaged pistons
without oil
Defective ring(s), valves,
Same as
cylinder head gasket or
without oil
piston is possible.
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
*****************************************************
Measurement steps:
G
Crank over the engine with the electric
starter (be sure the battery is fully charged)
with the throttle wide-open until the compres-
sion reading on the gauge stabilizes.
WARNING
When cranking the engine, ground the
spark plug lead to prevent sparking.
*****************************************************
7.Install:
Spark plug
G
3 - 25
CHK
ADJ
Diagnosis
2
, 188.31 psi)
2
, 163.57 psi)
2
, 210.50 psi)
18 Nm (1.8 m • kg, 13 ft • lb)