Yamaha Wolverine YX70EPNG, Service Manual

Page: 243 / 503

VALVES AND VALVE SPRINGS
5-30
TIP
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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a. Apply a coarse lapping compound “a” to the
valve face.
NOTICE
ECB01360
Do not let the lapping compound enter the
gap between the valve stem and the valve
guide.
b. Apply engine 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.
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.
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 impres-
sion.
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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EBS30144
CHECKING THE VALVE SPRINGS
The following procedure applies to all of the
valve springs.
1. Measure:
• Compressed valve spring force “a”
Out of specification
→
Replace the valve
spring.
Installed compression spring
force (intake)
134.00–154.00 N (13.66–15.70
kgf, 30.12–34.62 lbf)
Installed compression spring
force (exhaust)
107.00–123.00 N (10.91–12.54
kgf, 24.05–27.65 lbf)
Installed length (intake)
30.95 mm (1.22 in)
Installed length (exhaust)
32.20 mm (1.27 in)