Measuring The Compression Pressure - Yamaha 2010 XMAX YP125R Service Manual

EAS37P1093
MEASURING THE COMPRESSION
PRESSURE
TIP
Insufficient compression pressure will result in a
loss of performance.
1. Remove:
• Storage box
Refer to "GENERAL CHASSIS" on page 4-1.
2. Measure:
• Valve clearance
Out of specification → Adjust.
Refer to "ADJUSTING THE VALVE CLEAR-
ANCE" on page 3-6.
3. Start the engine, warm it up for several min-
utes, and then turn it off.
4. Disconnect:
• Spark plug cap
5. Remove:
• Spark plug
ECA37P1043
NOTICE
Before removing the spark plug, use com-
pressed air to blow away any dirt accumulat-
ed in the spark plug well to prevent it from
falling into the cylinder.
6. Install:
• Compression gauge "1"
Compression gauge
90890-03081
Engine compression tester
YU-33223
7. Measure:
• Compression pressure
Out of specification → Refer to steps (c) and
(d).
1
Standard compression pressure
(at sea level)
550 kPa/680 r/min (5.5
kgf/cm²/680 r/min, 78.2 psi/680
r/min)
Minimum–maximum
480–620 kPa (4.8–6.2 kgf/cm²,
68.3–88.2 psi)
M MMM M MMM M M MMM
a. Set the main switch to "ON".
b. With the throttle wide open, crank the engine
until the reading on the compression gauge
stabilizes.
EWA37P1019
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 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
L LLL L LLL L L LLL
8. Install:
• Spark plug
Spark plug
13 Nm (1.3 m·kgf, 9.4 ft·lbf)
9. Connect:
• Spark plug cap
10.Install:
• Storage box
Refer to "GENERAL CHASSIS" on page 4-1.
3-11
ENGINE (YP125R)
M M MMM M M MMM M
Diagnosis
Piston ring(s) wear or
damage → Repair.
Piston, valves, cylin-
der head gasket or
piston ring(s) possi-
bly defective → Re-
pair.
L L LLL L L LLL L
M MMM M MMM
L LLL L LLL