Yamaha YFM400FAR, Service Manual

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3 - 22
CHK
ADJ
MEASURING THE COMPRESSION PRESSURE
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.
*****************************************************
Measurement steps:
●
Crank over the engine with the electric
starter (be sure the battery is fully charged)
with the throttle wide-open until the
compression reading on the gauge
stabilizes.
WARNING
When cranking the engine, ground the
spark plug lead to prevent sparking.
*****************************************************
Compression pressure
(with oil introduced into cylinder)
Reading Diagnosis
Higher than
without oil
Worn or damaged pistons
Same as
without oil
Defective ring(s), valves,
cylinder head gasket or
piston is possible.
Compression pressure
(at sea level):
Standard:
1,400 kPa (14 kg/cm
2
, 203 psi)
Minimum:
1,218 kPa (12.2 kg/cm
2
, 177 psi)
Maximum:
1,568 kPa (15.7 kg/cm
2
, 227 psi)
8.Install:
●
Spark plug
9.Remove:
●
Fuel tank side panel (right)
●
Seat
Refer to “SEAT, CARRIERS, FENDERS
AND FUEL TANK”.
T
R
.
.
18 Nm (1.8 m • kg, 13 ft • lb)