Yamaha 5YF2-AE1, Service Manual, Page: 115 / 262

4 - 19
ENG
CAMSHAFT, ROCKER ARMS AND VALVES
8. Measure:
• valve seat width
a
Out of specification
→
Reface the valve
seat.
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a. Apply Mechanic’s blueing dye (Dykem)
b
to
the valve face.
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide and
onto the valve seat to make a clear pattern.
d. Measure the valve seat width. Where the
valve seat and valve face made contact,
blueing will have been removed.
e. If the valve seat is too wide, too narrow, or
the seat is not centered, the valve seat must
be refaced.
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Valve seat width
Intake
0.9 ~ 1.1 mm
(0.0354 ~ 0.0433 in)
<Limit>: 1.6 mm (0.063 in)
Exhaust
0.9 ~ 1.1 mm
(0.0354 ~ 0.0433 in)
<Limit>: 1.6 mm (0.063 in)
9. Lap:
• valve face
• valve seat
NOTE:
_
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
valve face.
CAUTION:
_
Do not let the compound enter the gap
between the valve stem and the guide.