Engine Inspection; Measure The Compression Pressure - Yamaha TMAX 2020 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:
• Bottom side cowling
• Side panel
• Radiator cover
Refer to "GENERAL CHASSIS (1)" on
page 4-1.
4. Disconnect:
• Spark plug cap
5. Remove:
• Spark plug
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:
• Compression gauge "1"
Compression gauge
90890-03081
Engine compression tester
YU-33223
1
ENGINE INSPECTION
7. Measure:
• Compression pressure
Out of specification  Refer to steps (c) and (d).
Compression pressure
1653–2128 kPa/360 r/min
(16.5–21.3 kgf/cm²/360 r/min,
235.1–302.7 psi/360 r/min)
a. Push the ON/start switch.
b. With the throttle wide open, crank the en-
gine until the reading on the compression
gauge stabilizes.
TIP
The difference in compression pressure be-
tween 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 Piston ring(s) wear or
Same as without oil
8. Install:
• Spark plugs
Spark plug
13 N·m (1.3 kgf·m, 9.6 lb·ft)
9. Connect:
• Spark plug cap
10.Install:
• Radiator cover
• Side panel
• Bottom side cowling
Refer to "GENERAL CHASSIS (1)" on
page 4-1.
5-6
Diagnosis
damage  Replace.
Piston, valves or cyl-
inder head gasket
possibly defective 
Replace.