Yamaha V Star 950 Service Manual page 212

7. Measure:
• Compression pressure
Out of specification → Refer to steps (c)
and (d).
Standard
sure (at sea level)
1400 kPa/400 r/min (14.0 kgf/
2
cm /400 r/min, 199.1 psi/400 r/
min)
Minimum–maximum
1250–1500 kPa (12.5–15.0 kgf/
2
cm , 177.8–213.3 psi)
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a. Set the main switch to "ON".
b. With the throttle wide open, crank the
engine until the reading on the compres-
sion gauge stabilizes.
TIP
The difference in compression pressure
between cylinders should not exceed 100 kPa
(1.0 kgf/cm², 14.5 psi).
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 pres-
Compression pressure (with oil applied into
the cylinder)
Reading
Higher than without
oil
Same as without oil
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8. Install:
• Spark plug
Spark plug
13 Nm (1.3 m·kgf, 9.4 ft·lbf)
9. Connect:
• Spark plug caps
10. Install:
• Rear cylinder right plastic cover
Refer to "ENGINE REMOVAL" on page 5-
1.
5-23
CYLINDER HEADS
Diagnosis
Piston ring(s) wear or
damage → Replace.
Piston, valves or cyl-
inder head gasket
possibly defective →
Replace.