Yamaha YZ450F(E) 2014, Owner'S Service Manual

Page: 222 / 360

VALVES AND VALVE SPRINGS
5-27
TIP
After replacing the valve guide, reface the valve
seat.
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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.
TIP
• When installing a new valve, always replace
the valve guide.
• If the valve is removed or replaced, always re-
place the oil seal.
EAS1SL1222
CHECKING THE 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 C “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 & 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
Valve margin thickness D (intake)
1.20 mm (0.0472 in)
Valve margin thickness D (ex-
haust)
0.85 mm (0.0335 in)
Valve stem runout
0.010 mm (0.0004 in)
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)