Yamaha YZ450F(D) Owner's Service Manual page 101

f. Apply Mechanic's blueing dye
(Dykem) to the valve face.
g. Install the valve into the cylinder
head.
h. Press the valve through the valve
guide and onto the valve seat to
make a clear pattern.
i. Measure the valve seat width
again. If the valve seat width is out
of specification, reface and relap
the valve seat.
CHECKING THE VALVE SPRINGS
1. Measure:
• Valve spring free length "a"
Out of specification → Replace.
Free length (valve
spring):
Intake:
40.76 mm (1.60 in)
<Limit>: 39.76 mm
(1.57 in)
Exhaust:
37.01 mm (1.46 in)
<Limit>: 36.01 mm
(1.42 in)
2. Measure:
• Compressed spring force "a"
Out of specification → Replace.
Compressed spring
force:
Intake:
178–204 N at 34.78
mm (18.2–20.8 kg at
34.78 mm, 40.01–
45.86 lb at 1.37 in)
Exhaust:
124–142 N at 30.83
mm (12.6–14.5 kg at
30.83 mm, 27.88–
31.92 lb at 1.21 in)
b. Installed length
VALVES AND VALVE SPRINGS
3. Measure:
• Spring tilt "a"
Out of specification → Replace.
Spring tilt limit:
Intake:
2.5°/1.8 mm (0.071 in)
Exhaust:
2.5°/1.6 mm (0.063 in)
CHECKING THE VALVE LIFTERS
1. Inspect:
• Valve lifter
Scratches/damage → Replace
both lifters and cylinder head.
INSTALLING THE VALVES
1. Apply:
• Molybdenum disulfide oil
Onto the valve stem and valve
stem seal.
2. Install:
• Valves "1"
• Valve spring seats "2"
• Valve stem seals "3"
• Valve springs "4"
• Valve spring retainers "5"
• Install the valve "a" with the identifi-
cation 33DI on the intake side and
the valve "b" with the identification
33DE on the exhaust side.
• Install the valve springs with the
larger pitch "c" facing upward.
4-20
d. Smaller pitch
3. Install:
• Valve cotters
Install the valve cotters by compress-
ing the valve spring with the valve
spring compressor "1" and the valve
spring compressor attachment "2".
Valve spring compres-
sor:
YM-04019/90890-04019
Valve spring compressor
attachment:
YM-04108/90890-04108
4. To secure the valve cotters onto
the valve stem, lightly tap the
valve tip with a piece of wood.
Hitting the valve tip with excessive
force could damage the valve.
5. Install:
• Adjusting pad "1"
• Valve lifter "2"
• Apply the molybdenum disulfide oil
on the valve stem end.
• Apply the engine oil on the valve lift-
ers.
• Valve lifter must turn smoothly
when rotated with a finger.
• Be careful to reinstall valve lifters
and pads in their original place.