Yamaha VMX12 2001 Service Manual page 85

MEASURING THE COMPRESSION PRESSURE
Compression pressure (at sea
level)
Minimum
1,200 kPa (12 kg/cm
Standard
1,400 kPa (14 kg/cm
Maximum
1,600 kPa (16 kg/cm
a. Set the main switch to "ON".
b. With the throttle wide open, crank the
engine until the reading on the compression
gauge stabilizes.
WARNING
@
To prevent sparking, ground all spark plug
leads before cranking the engine.
@
NOTE:
@
The difference in compression pressure
between cylinders should not exceed 100 kPa
2
(1 kg/cm , 1 bar).
@
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, squirt a few drops of
oil into the cylinder and measure again.
Refer to the following table.
Compression pressure
(with oil applied into the cylinder)
Reading
Higher than with-
out oil
Same as without oil
7. Install:
• spark plug
8. Connect:
• spark plug cap
3 - 18
CHK
ADJ
2
, 12 bar)
2
, 14 bar)
2
, 16 bar)
Diagnosis
Piston wear or
damage → Repair.
Piston ring(s),
valves, cylinder
head gasket or pis-
ton possibly defec-
tive → Repair.
18 Nm (1.8 m · kg)