Yamaha YZ450FA 2011, Owner'S Service Manual

Page: 137 / 318

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VALVES AND VALVE SPRINGS
5. Measure:
• Runout (valve stem)
Out of specification
→
Replace.
• When installing a new valve always replace
the guide.
• If the valve is removed or replaced always re-
place the oil seal.
6. Eliminate:
• Carbon deposits
(from the valve face and valve seat)
7. Inspect:
• Valve seat
Pitting/wear
→
Reface the valve seat.
8. Measure:
• Valve seat width "a"
Out of specification
→
Reface the valve seat.
Measurement steps:
a. Apply Mechanic's blueing dye (Dykem) "b"
to the valve face.
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 pattern.
d. Measure the valve seat width. Where the
valve seat and valve face made contact,
blueing will have been removed.
e. If the valve seat is too wide, too narrow, or
the seat is not centered, the valve seat must
be refaced.
9. Lap:
• Valve face
• Valve seat
This model uses titanium intake and ex-
haust valves. Titanium valves that have
been used to lap the valve seats must not be
used. Always replace lapped valves with
new valves.
•When replacing the cylinder head, replace the
valves without lapping the valve seats and
valve faces.
•When replacing the valves or valve guides,
use new valves to lap the valve seats, and
then replace them with new valves.
Lapping steps:
a. Apply a coarse lapping compound to the
valve face.
Do not let the compound enter the gap be-
tween the valve stem and the guide.
Runout limit:
0.01 mm (0.0004 in)
Valve seat width:
Intake:
0.9–1.1 mm (0.0354–0.0433 in)
<Limit>:1.6 mm (0.0630 in)
Exhaust:
0.9–1.1 mm (0.0354–0.0433 in)
<Limit>:1.6 mm (0.0630 in)