Yamaha YZ450FY 2009 Owner's Service Manual page 135

2. Replace:
• Valve guide
Replacement steps:
To ease guide removal, installation and to
maintain correct fit heat the cylinder head in an
over to 100 °C (212 °F).
a. Remove the valve guide using a valve guide
remover "1".
b. Install the new valve guide using a valve
guide remover "1" and valve guide installer
"2".
c. After installing the valve guide, bore the
valve guide using a valve guide reamer "3"
to obtain proper stem-to-guide clearance.
VALVES AND VALVE SPRINGS
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
After replacing the valve guide reface the valve
seat.
3. Inspect:
• Valve face
Pitting/wear → Grind the face.
• Valve stem end
Mushroom shape or diameter larger than
the body of the stem → Replace.
4. Measure:
• Margin thickness "a"
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)
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