Yamaha YFM45FAR Service Manual page 161

CAMSHAFT, ROCKER ARMS AND VALVES
*****************************************************
Measurement steps:
Apply Mechanic's blueing dye (Dykem) b to
G
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. Where the
valve seat and valve face made contact,
blueing will have been removed.
G
If the valve seat is too wide, too narrow, or
the seat is not centered, the valve seat must
be refaced.
*****************************************************
9.Lap:
Valve face
G
Valve seat
G
NOTE:
After refacing the valve seat or replacing the
valve and valve guide, the valve seat and
valve face should be lapped.
*****************************************************
Lapping steps:
G
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.
G
Apply molybdenum disulfide oil to the valve
stem.
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.
4 - 23
ENG