Yamaha YFM660FS Grizzly 4x4 Supplementary Service Manual page 242

VALVES AND VALVE SPRINGS
G
Install the valve into the cylinder head.
G
Turn the valve until the valve face and valve
seat are evenly polished, then clean off all of
the compound.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
G
Apply a fine lapping compound to the valve
face and repeat the above steps.
NOTE:
After every lapping operation be sure to clean
off all of the compound from the valve face and
valve seat.
G
Apply Mechanic's blueing dye (Dykem) to the
valve face.
G
Install the valve into the cylinder head.
G
Press the valve through the valve guide and
onto the valve seat to make a clear pattern.
G
Measure the valve seat width again. If the
valve seat width is out of specification, reface
and relap the valve seat.
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10.Measure:
Valve spring free length a
G
Out of specification → Replace.
4 - 29
ENG
Free length (valve spring):
Intake:
32.63 mm (1.28 in)
<Limit>: 31.0 mm (1.22 in)
Exhaust:
36.46 mm (1.44 in)
<Limit>: 34.6 mm (1.36 in)