Yamaha 2004 YP400 Service Manual page 239

VALVES AND VALVE SPRINGS
NOTE:
_
Where the valve seat and valve face contacted
one another, the blueing will have been
removed.
L
4. Lap:
NOTE:
_
After replacing the cylinder head or replacing
the valve and valve guide, the valve seat and
valve face should be lapped.
M
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 between your hands.
e. Apply a fine lapping compound to the valve
f. After every lapping procedure, be sure to
g. Apply Mechanic's blueing dye (Dykem) b
h. Install the valve into the cylinder head.
i. Press the valve through the valve guide and
5 - 26
LLL L LLL L L LLL L L LLL
• valve face
• valve seat
MMM M MMM M M MMM M M MMM
valve face.
CAUTION:
valve stem.
seat are evenly polished, then clean off all
of the lapping compound.
face and repeat the above steps.
clean off all of the lapping compound from
the valve face and valve seat.
onto the valve face.
onto the valve seat to make a clear impres-
sion.
ENG
L L LLL L L LLL L
M M MMM M M MMM M
LLL
MMM