Yamaha VMX12H, Supplementary Service Manual

Page: 100 / 405

COMPRESSION PRESSURE MEASUREMENT
COMPRESSION PRESSURE MEASUREMENT
NOTE:
Insufficient compression pressure will result in
performance loss.
1. Measure:
clearance
2.
Warm up the engine.
3.
Remove:
4.
Measure:
Out of specification Adjust.
plugs
pression pressure
By the following measurement steps.
Compression pressure measurement steps:
the Compression
33223)
using an adapter.
over the engine with the electric
starter (be sure the battery is fully charged)
with the throttle wide open until the com-
pression reading on the gauge stabilizes.
with specified levels
(See
chart)
Compression Pressure (at sea level):
980 (10 142 psi)
882 (9 128
psi)
(12 171
Standard:
Minimum:
Maximum:
When cranking the engine, ground
all of the
spark plug leads to prevent sparking.
the previous steps for the other
pressure falls bellow the minimum level:
cylinders.
1
)
Squirt a few drops of oil into the affected
cy
I inder
.
2)
Measure the compression again.
Compression Pressure
(with oil introduced into
Diagnosis
pistons
2-17