Yamaha YZ450FA 2011, Owner'S Service Manual

Page: 135 / 318

4-24
VALVES AND VALVE SPRINGS
REMOVING THE VALVE LIFTER AND
VALVE COTTER
1. Remove:
• Valve lifter "1"
• Pad "2"
Identify each lifter "1" and pad "2" position very
carefully so that they can be reinstalled in their
original place.
2. Check:
• Valve sealing
Leakage at the valve seat
→
Inspect 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 properly.
There should be no leakage at the valve
seat "2".
3. Remove:
• Valve cotter
Remove the valve cotters by compressing the
valve spring with the valve spring compressor
"1" and the valve spring compressor attach-
ment "2".
CHECKING THE VALVE
1. Measure:
• Stem-to-guide clearance
Out of specification
→
Replace the valve
guide.
Valve spring compressor:
YM-04019/90890-04019
Valve spring compressor attach-
ment:
YM-04108/90890-04108
Stem-to-guide clearance = valve guide in-
side diameter "a" - valve stem diameter
"b"
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)