Yamaha YZ450F(Y Owner's Manual page 95

CHECKING THE VALVE SPRINGS
1. Measure:
• Valve spring free length "a"
Out of specification → Replace.
Free length (valve
spring):
Intake:
37.03 mm (1.46 in)
<Limit>: 36.03 mm
(1.42 in)
Exhaust:
37.68 mm (1.48 in)
<Limit>: 36.68 mm
(1.44 in)
2. Measure:
• Compressed spring force "a"
Out of specification → Replace.
Compressed spring
force:
Intake:
111.3–127.9 N at 27.87
mm (11.3–13.0 kg at
27.87 mm, 24.91–
28.66 lb at 1.10 in)
Exhaust:
127.4–146.4 N at 27.38
mm (13.0–14.9 kg at
27.38 mm, 28.66–
32.85 lb at 1.08 in)
b. Installed length
3. Measure:
• Spring tilt "a"
Out of specification → Replace.
Spring tilt limit:
Intake:
2.5°/1.61 mm (0.063
in)
Exhaust:
2.5°/1.65 mm (0.065
in)
VALVES AND VALVE SPRINGS
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"
• Make sure that each valve is in-
stalled in its original place, also re-
ferring to the painted color as
follows.
Intake (middle) "a": blue
Intake (right/left) "b": gray
Exhaust "c": brown
• Install the valve springs with the
larger pitch "d" facing upward.
e. Smaller pitch
4-25
3. Install:
• Valve cotters
While compressing the valve spring
with a valve spring compressor "1" in-
stall the valve cotters.
Valve spring compres-
sor:
YM-4019/90890-04019
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.