Yamaha YZ450F(D) Owner's Service Manual page 99

REMOVING THE VALVE LIFTER
AND VALVE COTTER
1. Remove:
• Valve lifter "1"
• Pad "2"
Identify each lifter "1" and pad "2" po-
sition very carefully so that they can
be reinstalled in their original place.
2. Check:
• Valve sealing
Leakage at the valve seat → In-
spect the valve face, valve seat
and valve seat width.
Checking steps:
a. Pour a clean solvent "1" into the
intake and exhaust ports.
b. Check that the valve seals prop-
erly.
There should be no leakage at the
valve seat "2".
3. Remove:
• Valve cotter
Remove the valve cotters by com-
pressing the valve spring with the
valve spring compressor "1" and the
valve spring compressor attachment
"2".
VALVES AND VALVE SPRINGS
Valve spring compres-
sor:
YM-04019/90890-04019
Valve spring compressor
attachment:
YM-04108/90890-04108
CHECKING THE VALVE
1. Measure:
• Stem-to-guide clearance
Stem-to-guide clearance = valve
guide inside diameter "a" -
valve stem diameter "b"
Out of specification → Replace
the valve guide.
Clearance (stem to
guide):
Intake:
0.010–0.037 mm
(0.0004–0.0015 in)
<Limit>:0.08 mm
(0.003 in)
Exhaust:
0.020–0.047 mm
(0.0008–0.0019 in)
<Limit>:0.10 mm
(0.004 in)
2. Replace:
• Valve guide
Replacement steps:
To ease guide removal, installation
and to maintain correct fit heat the
cylinder head in an over to 100 °C
(212°F).
4-18
a. Remove the valve guide using a
valve guide remover "1".
b. Install the new valve guide using a
valve guide remover "1" and valve
guide installer "2".
Valve guide installation
height "a":
Intake:
15.1–15.5 mm (0.59–
0.61 in)
Exhaust:
12.2–12.6 mm (0.48–
0.50 in)
c. After installing the valve guide,
bore the valve guide using a valve
guide reamer "3" to obtain proper
stem-to-guide clearance.
Valve guide remover &
installer set (ø5.5):
90890-04016
Valve guide remover (5.5
mm):
YM-01122
Valve guide installer (5.5
mm):
YM-04015
Valve guide reamer (5.5
mm):
YM-01196
After replacing the valve guide reface
the valve seat.