Yamaha MZ250 Service Manual page 36

ENGINE INSPECTION
4. Measure:
9 Compression pressure
Crank the engine until the needle stop
rising on the compression gauge.
Out of specification → Refer to the
testing steps.
Standard compression pressure:
Refer to "SPECIFICATIONS" in
the Supplementary service
manual.
WARNING
To prevent sparking when cranking the
engine, ground the high tension cord.
Testing steps (below the minimum speci-
fication):
a. Squirt a few drops of oil into the cylin-
der.
b. Measure the compression again.
Reading
Higher than
without oil
Same as
without oil
Testing steps (above the maximum speci-
fication):
a. Check the cylinder head, valve surfac-
es, and piston crown for carbon depos-
its.
Carbon deposits → Eliminate.
5. Install:
9 Spark plug
Spark plug:
Refer to "TIGHTENING TORQUES"
in the Supplementary service
manual.
9 Spark plug cap
3-2
ENG
Diagnosis
9 Worn cylinder, piston, and
piston ring(s)
9 Defective piston, piston
ring(s), valve(s), and cyl-
inder head gasket
9 Improper valve timing and
valve clearance