Yamaha MX250 - Valve Lapping

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ENGINE
VALVE
3.
Insert the valve into the valve guide and use a valve
lapper to contact the valve face with the valve seat.
TIP
Do not rotate the valve while the valve face is contacting
the valve seat.
4.
Measure:
• Valve face contact width “a”
Make sure that the contact width along the entire
valve face is within specifications.
Out of specification/rough/eccentric wear 
Replace.
5.
Measure:
• Valve seat contact width “a”
Make sure that the contact width along the entire
valve seat is within specifications.
Out of specification/rough/eccentric wear 
Replace.
VALVE LAPPING
1.
Apply a coarse lapping compound evenly on the valve
face. Lap the valve by tapping and rotating the valve
lapper “1” clockwise and counterclockwise.
a
Valve face contact width (Intake):
0.7–0.9 mm (0.0276–0.0354 in)
Valve face contact width (Exhaust):
0.7–0.9 mm (0.0276–0.0354 in)
Limit (Intake):
1.4 mm (0.055 in)
Limit (Exhaust):
1.4 mm (0.055 in)
a
Valve seat contact width (Intake):
0.7–0.9 mm (0.0276–0.0354 in)
Valve seat contact width (Exhaust):
0.7–0.9 mm (0.0276–0.0354 in)
Limit (Intake):
1.4 mm (0.055 in)
Limit (Exhaust):
1.4 mm (0.055 in)
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