Engine Inspection; Measuring The Compression Pressure - Yamaha 2012 TMAX XP500A Service Manual

EAS59C1501

ENGINE INSPECTION

EAS59C1502
MEASURING THE COMPRESSION PRES-
SURE
The following procedure applies to all of the
cylinders.
TIP
Insufficient compression pressure will result in
a loss of performance.
1. Measure:
• Valve clearance
Out of specification → Adjust.
Refer to "ADJUSTING THE VALVE
CLEARANCE" on page 3-5.
2. Start the engine, warm it up for several
minutes, and then turn it off.
3. Remove:
• Radiator cover
Refer to "GENERAL CHASSIS" on page
4-1.
4. Disconnect:
• Spark plug caps
5. Remove:
• Spark plugs
ECA13340
Before removing the spark plugs, use com-
pressed air to blow away any dirt accumu-
lated in the spark plug wells to prevent it
from falling into the cylinders.
6. Install:
• Compression gauge "1"
Compression gauge
90890-03081
Engine compression tester
YU-33223
ENGINE INSPECTION
7. Measure:
• Compression pressure
Out of specification → Refer to steps (c)
and (d).
Standard
sure (at sea level)
1950 kPa/470 r/min (19.5 kgf/
cm²/470 r/min, 282.8 psi/470 r/
min)
Minimum–maximum
1700–2180
(17.0–21.8 kgf/cm²/470 r/min,
246.1–316.8 psi/470 r/min)
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
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 kgf/cm², 14 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 pressure (with oil applied into
the cylinder)
Reading
Higher than without
oil
Same as without oil
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
8. Install:
• Spark plugs
Spark plug
13 Nm (1.3 m·kgf, 9.4 ft·lbf)
5-1
compression pres-
kPa/470 r/min
Diagnosis
Piston ring(s) wear or
damage → Replace.
Piston, valves or cyl-
inder head gasket
possibly defective →
Replace.