Yamaha XG250, Service Manual

Page: 162 / 278

VALVES AND VALVE SPRINGS
5-20
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3. Eliminate:
●
Carbon deposits
(from the valve face and valve seat)
4. Check:
●
Valve face
Pitting/wear
→
Grind the valve face.
●
Valve stem end
Mushroom shape or diameter larger than the
body of the valve stem
→
Replace the valve.
5. Measure:
●
Valve margin thickness D “a”
Out of specification
→
Replace the valve.
6. Measure:
●
Valve stem runout
Out of specification
→
Replace the valve.
NOTE:
●
When installing a new valve, always replace
the valve guide.
●
If the valve is removed or replaced, always re-
place the oil seal.
EAS24300
CHECKING THE VALVE SEATS
The following procedure applies to all of the
valves and valve seats.
1. Eliminate:
●
Carbon deposits
(from the valve face and valve seat)
2. Check:
●
Valve seat
Pitting/wear
→
Replace the cylinder head.
3. Measure:
●
Valve seat width “a”
Out of specification
→
Replace the cylinder
head.
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a. Apply Mechanic’s blueing dye (Dykem) “b”
onto the valve face.
Valve guide remover (
ø
6)
90890-04064
Valve guide remover (6.0 mm)
YM-04064-A
Valve guide installer (
ø
6)
90890-04065
Valve guide installer (6.0 mm)
YM-04065-A
Valve guide reamer (
ø
6)
90890-04066
Valve guide reamer (6.0 mm)
YM-04066
Valve margin thickness
Valve margin thickness D (intake)
0.80
–
1.20 mm (0.0315
–
0.0472 in)
Valve margin thickness D (ex-
haust)
0.80 – 1.20 mm (0.0315 – 0.0472 in)
a
Valve stem runout
Valve stem runout
0.030 mm (0.0012 in)
Valve seat width
Valve seat width C (intake)
0.90 – 1.10 mm (0.0354 – 0.0433 in)
Valve seat width C (exhaust)
0.90 – 1.10 mm (0.0354 – 0.0433 in)
a