Yamaha YZ450F Manuel D'atelier Du Proprietaire page 314

VALVES AND VALVE SPRINGS
5. Measure:
NOTE:
• When installing a new valve always replace
the guide.
• If the valve is removed or replaced always
replace the oil seal.
6. Eliminate:
7. Inspect:
8. Measure:
Measurement steps:
• Apply Mechanic's blueing dye (Dykem) b
• Install the valve into the cylinder head.
• Press the valve through the valve guide
• Measure the valve seat width. Where the
• If the valve seat is too wide, too narrow, or
4 - 37
• Runout (valve stem)
Out of specification → Replace.
Runout limit:
0.01 mm (0.0004 in)
• Carbon deposits
(from the valve face and valve seat)
• Valve seats
Pitting/wear → Reface the valve seat.
• Valve seat width a
Out of specification → Reface the valve
seat.
Valve seat width:
Intake:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
<Limit>: 1.6 mm (0.0630 in)
Exhaust:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
<Limit>: 1.6 mm (0.0630 in)
to the valve face.
and onto the valve seat to make a clear
pattern.
valve seat and valve face made contact,
blueing will have been removed.
the seat is not centered, the valve seat
must be refaced.
ENG