Yamaha YZ 2017 Series, Owner'S Service Manual

Page: 229 / 410

VALVES AND VALVE SPRINGS
5-28
d. Turn the valve until the valve face and the
valve seat are evenly polished, then clean
off all of the lapping compound.
TIP
While turning the valve lapper, tap and lap the
valve seat.
e. Apply a fine lapping compound to the valve
face, and repeat the above steps.
f. After every lapping step, be sure to clean off
all of the lapping compound from the valve
face and the valve seat.
g. Apply Mechanic’s blueing dye (Dykem) “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 contact width “c”
again. If the valve seat contact width is out of
specification, reface and lap the valve seat.
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EASB29B226 CHECKING THE VALVE SPRINGS
1. Measure:
• Valve spring free length “a”
Out of specification

Replace the valve
spring.
2. Measure:
• Compressed valve spring force “a”
Out of specification

Replace the valve
spring.
Free length (intake)
39.03 mm (1.54 in)
Limit
37.08 mm (1.46 in)
Free length (exhaust)
35.59 mm (1.40 in)
Limit
33.81 mm (1.33 in)
b. Installed length
Installed compression spring
force (intake)
155.00–179.00 N (15.81–18.25
kgf, 34.84–40.24 lbf)
Installed compression spring
force (exhaust)
137.00–157.00 N (13.97–16.01
kgf, 30.80–35.29 lbf)
Installed length (intake)
32.50 mm (1.28 in)
Installed length (exhaust)
29.60 mm (1.17 in)