Yamaha T135SE Service Manual page 70

MEASURING THE COMPRESSION PRESSURE
YamahaT135.COM
Yamaha T135 Service Manual
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3-16
6. Install:
9compression gauge 1
Compression gauge
90890-03081
7. Measure:
9compression pressure
Out of specification → Refer to steps (c)
and (d).
Compression pressure
(at sea level)
Minimum
490 kPa (4.9 kg/cm
Standard
560 kPa (5.6 kg/cm
Maximum
630 kPa (6.3 kg/cm
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a. Set the main switch to "ON".
b. With the throttle wide open and push the
"START" switch, then crank the engine until
the reading on the compression gauge sta-
bilizes.
w
To prevent sparking, ground the spark plug
lead before cranking the engine.
c. If the compression pressure is above the
maximum specification, check the cylinder
head, valve surfaces, and piston crown for
carbon deposits.
Carbon deposits → Eliminate.
d. If the compression pressure is below the
minimum specification, pour a teaspoonful
of engine oil into the spark plug bore and
measure again.
Refer to the following table.
Compression pressure
(with oil applied into the cylinder)
Reading
Higher than with-
out oil
Same as without
oil
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CHK
ADJ
2 , 70 psi)/at 500 r/min
2 , 80 psi)/at 500 r/min
2 , 90 psi)/at 500 r/min
Diagnosis
Piston ring(s) wear
or damage → →
Repair.
Piston, valves, cyl-
inder head gasket
or piston possibly
defective → → Repair.