Yamaha YZ450F(S) Owner's Service Manual page 310

VALVES AND VALVE SPRINGS
NOTE:
After replacing the valve guide reface the
valve seat.
3. Inspect:
4. Measure:
4 - 36
Valve guide remover:
Intake: 4.5 mm (0.18 in)
YM-4116/90890-04116
Exhaust: 5.0 mm (0.20 in)
YM-4097/90890-04097
Valve guide installer:
Intake:
YM-4117/90890-04117
Exhaust:
YM-4098/90890-04098
Valve guide reamer:
Intake: 4.5 mm (0.18 in)
YM-4118/90890-04118
Exhaust: 5.0 mm (0.20 in)
YM-4099/90890-04099
Valve face
G
Pitting/wear → Grind the face.
Valve stem end
G
Mushroom shape or diameter larger
than the body of the stem → Replace.
Margin thickness a
G
Out of specification → Replace.
Margin thickness:
Intake:
1.0 mm (0.039 in)
<Limit>: 0.85 mm (0.033 in)
Exhaust:
1.0 mm (0.039 in)
<Limit>: 0.85 mm (0.033 in)
ENG