Measuring The Compression Pressure - Yamaha XT660Z 2008 Service Manual

EAS00067
MEASURING THE COMPRESSION
PRESSURE
NOTE:
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 3-3.
2. Start the engine, warm it up for several min-
utes, and then turn it off.
3. Disconnect:
• Spark plug cap
4. Remove:
• Spark plug
CAUTION:
Before removing the spark plug, blow away
any dirt accumulated in the spark plug well
with compressed air to prevent it from
falling into the cylinder.
5. Install:
• Compression gauge "1"
• Adaptor (compression gauge) "2"
Compression gauge
90890-03081
Adaptor (compression gauge)
90890-04082
1
6. Measure:
• Compression pressure
Out of specification → Refer to steps (c) and
(d).
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a. Set the main switch to "ON" and the engine
stop switch to "I".
b. With the throttle wide open, crank the engine
until the reading on the compression gauge
stabilizes.
WARNING
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 it again.
Refer to the following table.
Compression pressure (with oil applied into
the cylinder)
Reading
Higher than without
oil
2
Same as without oil
7. Install:
• Spark plug
8. Connect:
• Spark plug cap
3-8
Compression pressure
(at sea level)
Minimum
600 kPa (6.0 kg/cm
Standard
650 kPa (6.5 kg/cm
Maximum
700 kPa (7.0 kg/cm
Diagnosis
Piston ring(s) worn
or damaged →Repair.
Piston, valves,
cylinder head gasket
or piston possibly
defective → Repair.
Spark plug
13 Nm (1.3 m·kg, 9.4 ft·lb)
ENGINE
2 , 85.3 psi)
2 , 92.4 psi)
2 , 99.6 psi)