Engine Inspection; Measuring The Compression Pressure - Yamaha MBK X-MAX 300 2017 Service Manual

EAS20041

ENGINE INSPECTION

EAS30249
MEASURING THE COMPRESSION
PRESSURE
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:
• Storage box
Refer to "GENERAL CHASSIS (4)" on page
4-10.
4. Disconnect:
• Spark plug cap
5. Remove:
• Spark plug
ECA20470
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
1
7. Measure:
• Compression pressure
Out of specification → Refer to steps (c) and
(d).
ENGINE INSPECTION
Compression pressure
783–1008 kPa/860 r/min (7.8–
10.1 kgf/cm²/860 r/min, 111.4–
143.4 psi/860 r/min)
a. Turn the main switch to "ON".
b. With the throttle wide open, crank the en-
gine until the reading on the compression
gauge stabilizes.
EWA12960
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
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 plug "1"
Spark plug
13 N·m (1.3 kgf·m, 9.6 lb·ft)
TIP
When tightening the spark plug, make sure that
the inside "a" of the spark plug wrench "2" does
not contact the portion "b" of the spark plug.
a
5-5
Diagnosis
Piston ring(s) wear or
damage → Repair.
Piston, valves, cylinder
head gasket or piston
ring(s) possibly defec-
tive → Repair.
b
2
1