Yamaha WR450FB 2012 Owner's Service Manual page 230

VALVES AND VALVE SPRINGS
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a. Apply Mechanic's blueing dye (Dykem) "b"
onto the valve face.
b
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide and
onto the valve seat to make a clear impres-
sion.
d. Measure the valve seat width "a".
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Where the valve seat and valve face contacted
one another, the blueing will have been re-
moved.
After replacing the cylinder head or replacing
the valve and valve guide, the valve seat and
valve face should be lapped.
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ECA10X1018
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This model uses titanium intake valves.
Titanium valves that have been used to lap
the valve seats must not be used.Always re-
place lapped valves with new valves.
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• When replacing the cylinder head, replace the
valves without lapping the valve seats and
valve faces.
• When replacing the valves or valves guides,
use new valves to lap the valve seats, and
then replace them with new valves.
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a. Apply a coarse lapping compound "a" to the
valve face.
ECA13790
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not let the lapping compound enter the
gap between the valve stem and the valve
guide.
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.
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For the best lapping results, lightly tap the valve
seat while turning 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 Mechanic's blueing dye (Dykem) "b"
onto the valve face.