Yamaha YZ250F(N)/LC Owner's Service Manual page 324

VALVES AND VALVE SPRINGS
NOTE:
After replacing the valve guide reface the
valve seat.
3. Inspect:
4. Measure:
4 - 35
Valve guide remover:
Intake 4.0 mm (0.16 in)
YM-4111/90890-04111
Exhaust 4.5 mm (0.18 in)
YM-4116/90890-04116
Valve guide installer:
Intake 4.0 mm (0.16 in)
YM-4112/90890-04112
Exhaust 4.5 mm (0.18 in)
YM-4117/90890-04117
Valve guide reamer:
Intake 4.0 mm (0.16 in)
YM-4113/90890-04113
Exhaust 4.5 mm (0.18 in)
YM-4118/90890-04118
Valve face
Pitting/wear Grind the face.
Valve stem end
Mushroom shape or diameter larger
than the body of the stem
Margin thickness a
Out of specification
Margin thickness:
Intake:
0.7 mm (0.0276 in)
Exhaust:
0.7 mm (0.0276 in)
ENG
Replace.
Replace.