Yamaha TW125 1999 Service Manual page 115

VALVES AND VALVE SPRINGS
a. Apply Mechanic's blueing dye (Dykem) 1
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
4. Lap:
NOTE:
After replacing the cylinder head or replacing
the valve and valve guide, the valve seat and
valve face should be lapped.
a. Apply a coarse lapping compound a to the
Do not let the lapping compound enter the
gap between the valve stem and the valve
guide.
b. Apply molybdenum disulfide oil onto the
c. Install the valve into the cylinder head.
d. Turn the valve until the valve face and valve
NOTE:
For the best lapping results, lightly tap the valve
seat while rotating the valve back and forth be-
tween your hand.
4-21
onto the valve face.
onto the valve seat to make a clear pattern.
valve seat and valve face contacted one
another, the blueing will have been removed.
S valve face
S valve seat
valve face.
CAUTION:
valve stem.
seat are evenly polished, then clean off all of
the lapping compound.
ENG