Yamaha MX250 - Checking the Cylinder and Piston

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ENGINE
PISTON, CAMSHAFT, CRANKCASE, AND CRANKSHAFT
CHECKING THE CYLINDER AND PISTON
1.
Check:
• Piston wall
• Cylinder wall
Vertical scratches  Replace the cylinder, and
replace the piston and piston rings as a set.
2.
Measure:
• Cylinder warpage
TIP
Measure the warpage on the contact surface of the cylin-
der head at six points using a straight edge and feeler
gauge set.
Out of specification  Replace the crankcase
assembly.
3.
Measure:
• Piston-to-cylinder clearance
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Measure cylinder bore “C” with the cylinder bore
gauge.
TIP
Measure cylinder bore “C” by taking side-to-side and front-
to-back measurements of the cylinder.
Feeler gauge set:
YU-26900-9
Thickness gauge:
90890-03180
Warpage limit:
0.05 mm (0.002 in)
Bore:
80.000–80.020 mm (3.1496–3.1503 in)
Warpage limit:
80.04 mm (3.1512 in)