Engine Inspection; Measuring The Compression Pressure - Yamaha STAR XVS95CE 2DX1 2014 Service Manual

EAS1TP1047

ENGINE INSPECTION

EAS20710
MEASURING THE COMPRESSION
PRESSURE
The following procedure applies to all of the cyl-
inders.
TIP
Insufficient compression pressure will result in a
loss of performance.
1. Measure:
• Valve clearance
Out of specification → Adjust.
Refer to "ADJUSTING THE VALVE CLEAR-
ANCE" on page 3-4.
2. Start the engine, warm it up for several min-
utes, and then turn it off.
3. Remove:
• Rear cylinder right cover
Refer to "ENGINE REMOVAL" on page 5-3.
4. Disconnect:
• Spark plug caps
5. Remove:
• Spark plug
ECA13340
NOTICE
Before removing the spark plugs, use com-
pressed air to blow away any dirt accumulat-
ed in the spark plug wells to prevent it from
falling into the cylinders.
6. Install:
• Compression gauge "1"
• Extension "2"
Compression gauge
90890-03081
Engine compression tester
YU-33223
Extension
90890-04136
2
1
ENGINE INSPECTION
7. Measure:
• Compression pressure
Out of specification → Refer to steps (c) and
(d).
Standard compression pressure
(at sea level)
1400 kPa/400 r/min (14.0
kgf/cm²/400 r/min, 199.1 psi/400
r/min)
Minimum-maximum
1250–1500 kPa (12.5–15.0
kgf/cm², 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 compression gauge
stabilizes.
TIP
The difference in compression pressure be-
tween 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 min-
imum specification, pour a teaspoonful of en-
gine 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 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
5-1
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Diagnosis
Piston ring(s) wear or
damage → Replace.
Piston, valves or cyl-
inder head gasket
possibly defective →
Replace.
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