Checking The Valve Seats - Yamaha YZ450FX 2019 Owner's Service Manual

c. After installing the valve guide, expand the
hole in the valve guide with the valve guide
remover & installer set (ø5.5) "3" to obtain the
proper valve-stem-to-valve-guide clearance.
TIP
After replacing the valve guide, reface the valve
seat.
Valve guide remover & installer
set (ø5.5)
90890-04016
Valve guide remover (5.5 mm)
YM-01122
Valve guide installer (ø5.5)
90890-04015
Valve guide installer (5.5 mm)
YM-04015
Valve guide reamer (5.5 mm)
90890-01196
Valve guide reamer (5.5 mm)
YM-01196
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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.
2 2 2
1 1
5-27
VALVES AND VALVE SPRINGS
5. 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 valve stem seal.
Valve stem runout
0.010 mm (0.0004 in)
EAM30092

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 contact width "a"
Out of specification  Replace the cylinder
head.
Valve seat contact width (intake)
0.90–1.10 mm (0.0354–0.0433 in)
Limit
1.5 mm (0.06 in)
Valve seat contact width (ex-
haust)
0.90–1.10 mm (0.0354–0.0433 in)
Limit
1.5 mm (0.06 in)