Yamaha MX250 - Checking the Crankcase

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ENGINE
PISTON, CAMSHAFT, CRANKCASE, AND CRANKSHAFT
b. If out of specification, replace the crankcase
assembly, and replace the piston and piston rings
as a set.
c. Measure piston skirt diameter “P” with the microm-
eter.
a = 10 mm (0.4 in) from the piston bottom edge
d. If out of specification, replace the piston and piston
rings as a set.
e. Calculate the piston-to-cylinder clearance with the
following formula.
f. If out of specification, replace the crankcase
assembly, and replace the piston and piston rings
as a set.
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CHECKING THE CRANKCASE
1.
Check:
•Crankcase
Damage  Replace.
• Bearing
Noise/wear/rotational failure  Replace.
“C” = maximum of D
1
, D
2
, D
3
, D
4
, D
5
, D
6
P
a
Piston diameter:
79.96–79.98 mm (3.1480–3.1488 in)
Limit:
79.91 mm (3.1461 in)
Piston-to-cylinder clearance = Cylinder bore “C” – Piston skirt
diameter “P”
Piston-to-cylinder clearance:
0.033–0.047 mm (0.0012–0.0018 in)
Limit:
0.06 mm (0.0024 in)