Yamaha YZ450FF 1SL-28199-11, Owner'S Service Manual

Page: 225 / 358

VALVES AND VALVE SPRINGS
5-30
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 width “c” again. If the
valve seat width is out of specification,
reface and lap the valve seat.
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EAS1SL5225 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.
3. Measure:
• Valve spring tilt “a”
Out of specification

Replace the valve
spring.
Free length (intake)
40.76 mm (1.60 in)
Limit
39.76 mm (1.57 in)
Free length (exhaust)
37.01 mm (1.46 in)
Limit
36.01 mm (1.42 in)
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)
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)