Yamaha XP500 Service Manual page 150

MEASURING THE COMPRESSION PRESSURE
M MMM M MMM M M MMM
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
between cylinders should not exceed 100 kPa
2
(1 kg/cm , 14.22 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
engine of 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 with-
out oil
Same as without
oil
L LLL L LLL L L LLL
8. Install:
• spark plug
9. Connect:
• spark plug cap
10.Install:
• inner fender
• footrest board (left and right)
Refer to "SIDE COVER MOULDINGS AND
LEG SHIELD".
3 - 29
CHK
ADJ
M M MMM M M MMM M
in compression pressure
Diagnosis
Piston wear or
damage → Repair.
Piston ring(s),
valve(s), cylinder
head gasket or pis-
ton possibly defec-
tive → Repair.
L L LLL L L LLL L
13 Nm (1.3 m · kg, 9.4 ft · lb)
M MMM M MMM
L LLL L LLL