Yamaha YFM45FAR Service Manual page 91

MEASURING THE COMPRESSION PRESSURE
7.Measure:
Compression pressure
G
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.
G
Compression pressure
(with oil introduced into cylinder)
Reading
Higher than
without oil
Same as
without oil
Compression pressure
(at sea level):
Standard:
1,270 kPa (12.7 kg/cm
Minimum:
1,105 kPa (11.1 kg/cm
Maximum:
1,422 kPa (14.2 kg/cm
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Measurement steps:
G
Crank over the engine with the electric
starter (be sure the battery is fully charged)
with the
compression
stabilizes.
WARNING
When cranking the engine, ground the
spark plug lead to prevent sparking.
*****************************************************
8.Install:
Spark plug
G
9.Remove:
Fuel tank side panel (right)
G
Seat
G
Refer to "SEAT, CARRIERS, FENDERS
AND FUEL TANK".
3 - 22
CHK
ADJ
Diagnosis
Worn or damaged pistons
Defective ring(s), valves,
cylinder head gasket or
piston is possible.
throttle wide-open
reading on the
18 Nm (1.8 m • kg, 13 ft • lb)
2
, 181 psi)
2
, 158 psi)
2
, 202 psi)
until the
gauge