Engine Inspection; Measure The Compression Pressure - Yamaha MT-09 2021 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.
• Fuel tank center cover
Refer to "GENERAL CHASSIS (1)" on
page 4-1.
• Fuel tank
Refer to "FUEL TANK" on page 7-1.
• Air filter case
Refer to "GENERAL CHASSIS (2)" on
page 4-10.
• Ignition coil
• Spark plug
Refer to "CAMSHAFTS" on page 5-16.
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.
4. Install:
• Compression gauge "1"
• Extension "2"
Compression gauge
90890-03081
Engine compression tester
YU-33223
Compression gauge extension
122mm
90890-04136
Compression gauge extension
122mm
YM-04136
ENGINE INSPECTION
1
5. Measure:
• Compression pressure
Out of specification → Refer to steps (c) and
(d).
Compression pressure
1365–1758 kPa/600 r/min
(13.7–17.6 kgf/cm²/600 r/min,
194.3–250.1 psi/600 r/min)
a. Set the main switch to "ON".
b. With the throttle wide open, crank the en-
gine until the reading on the compression
gauge stabilizes.
EWA17100
WARNING
To prevent sparking the plug, remove all ig-
nition coil couplers and fuel injector cou-
plers before cranking the engine.
TIP
The difference in compression pressure be-
tween cylinders should not exceed 100 kPa (1
kg/cm², 15 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.
5-7
2