Yamaha YFZ450S 2003 Service Manual page 173

VALVES AND VALVE SPRINGS
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a. Apply Mechanic's blueing dye (Dykem) b to
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide and
d. Measure the valve seat width. Where the
e. If the valve seat is too wide, too narrow, or
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9. Lap:
NOTE:
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After refacing the valve seat or replacing the
valve and valve guide, the valve seat and
valve face should be lapped.
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a. Apply a coarse lapping compound to the
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Do not let the compound enter the gap
between the valve stem and the valve
guide.
b. Apply molybdenum disulfide oil to the valve
c. Install the valve into the cylinder head.
d. Turn the valve until the valve face and valve
NOTE:
_
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
e. Apply a fine lapping compound to the valve
NOTE:
_
After every lapping operation be sure to clean
off all of the compound from the valve face and
valve seat.
4 - 30
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the valve face.
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.
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• valve face
• valve seat
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valve face.
CAUTION:
stem.
seat are evenly polished, then clean off all
of the compound.
face and repeat the above steps.
ENG
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