Yamaha YFM7FGPW Service Manual page 187

VALVES AND VALVE SPRINGS
4. Measure:
• margin thickness a
Out of specification → Replace.
5. Measure:
• valve stem runout
Out of specification → Replace.
NOTE:
_
• When installing a new valve, always replace
the valve guide.
• If the valve is removed or replaced, always
replace the valve stem seal.
6. Eliminate:
• carbon deposits
(from the valve face and valve seat)
7. Check:
• valve seats
Pitting/wear → Reface the valve seat.
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.
4 - 29
ENG
Margin thickness
0.80 ~ 1.20 mm
(0.0315 ~ 0.0472 in)
Runout limit
0.040 mm (0.0016 in)
Valve seat width
1.00 ~ 1.20 mm
(0.0394 ~ 0.0472 in)
<Limit>: 1.60 mm (0.0630 in)
M MMM M M MMM M M MMM M M MMM M M MMM M MMM