Checking The Valve Springs - Yamaha YZ450F Owner's Service Manual

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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EASB111222

CHECKING THE VALVE SPRINGS

1. Measure:
• Valve spring free length "a"
Out of specification  Replace the valve
spring.
Free length (intake)
40.76 mm (1.60 in)
Limit
38.72 mm (1.52 in)
Free length (exhaust)
36.94 mm (1.45 in)
Limit
35.09 mm (1.38 in)
VALVES AND VALVE SPRINGS
2. Measure:
• Compressed valve spring force "a"
Out of specification  Replace the valve
spring.
b. Installed length
Installed compression spring
force (intake)
178.00–204.00 N (18.15–20.80
kgf, 40.01–45.86 lbf)
Installed compression spring
force (exhaust)
124.00–142.00 N (12.64–14.48
kgf, 27.88–31.92 lbf)
Installed length (intake)
34.78 mm (1.37 in)
Installed length (exhaust)
30.83 mm (1.21 in)
3. Measure:
• Valve spring tilt "a"
Out of specification  Replace the valve
spring.
Spring tilt (intake)
2.5 °/1.8 mm (2.5 °/0.07 in)
Spring tilt (exhaust)
2.5 °/1.6 mm (2.5 °/0.06 in)
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