Yamaha R15 2022 Service Manual page 261

TIP
Where the valve seat and valve face contacted
one another, the blue layout fluid will have been
removed.
4. Lap:
• Valve face
• Valve seat
TIP
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 valve face.
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Do not let the lapping compound enter the
gap between the valve stem and the valve
guide.
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b. Apply molybdenum disulfide oil onto the
valve stem.
c. Install the valve into the cylinder head.
d. Turn the valve until the valve face and
valve seat are evenly polished, then clean
off all of the lapping compound.
VALVES AND VALVE SPRINGS
5-24
TIP
For the best lapping results, lightly tap the valve
seat while rotating the valve back and forth be-
tween your hands.
e. Apply a fine lapping compound to the
valve face and repeat the above steps.
f. After every lapping procedure, be sure to
clean off all of the lapping compound from
the valve face and valve seat.
g. Apply blue layout fluid "b" onto the valve
face.
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h. Install the valve into the cylinder head.
i. Press the valve through the valve guide
and onto the valve seat to make a clear
impression.
j. Measure the valve seat width "c" again. If
the valve seat width is out of specification,
reface and lap the valve seat.
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ENG