Engine Inspection; Measure The Compression Pressure - Yamaha YZF-R25 Service Manual

EAS20041

ENGINE INSPECTION

EAS30249

MEASURE 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 3-5.
2. Start the engine, warm it up for several min-
utes, and then turn it off.
3. Remove:
• Rider seat
Refer to "GENERAL CHASSIS (1)" on page
4-1.
• Side panels
Refer to "GENERAL CHASSIS (2)" on page
4-3.
• Fuel tank cover assembly
Refer to "GENERAL CHASSIS (3)" on page
4-5.
• Fuel tank
Refer to "FUEL TANK" on page 7-1.
4. Disconnect:
• Spark plug caps "1"
5. Remove:
• Spark plugs
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:
• Extension "1"
• Compression gauge "2"
1
5-1
ENGINE INSPECTION
Extension
90890-04136
Compression gauge
90890-03081
Engine compression tester
YU-33223
2
7. Measure:
• Compression pressure
Out of specification → Refer to steps (c) and
(d).
Standard compression pressure
(at sea level)
**
Minimum-maximum
**
▼ ▼▼▼ ▼ ▼▼▼ ▼ ▼ ▼▼▼ ▼
a. Turn the main switch to "ON".
b. With the throttle wide open, crank the engine
until the reading on the compression gauge
stabilizes.
EWA12940
WARNING
To prevent sparking, ground all spark plug
leads before cranking the engine.
TIP
The difference in compression pressure be-
tween cylinders should not exceed 100 kPa (1
kg/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 min-
imum specification, pour a teaspoonful of en-
gine oil into the spark plug bore and measure
again.
Refer to the following table.
1
▼ ▼▼▼ ▼ ▼ ▼▼▼ ▼ ▼ ▼▼▼ ▼ ▼▼▼