Checking The Valve Seats - Yamaha YZ250FM 2021 Owner's Service Manual

Intake
Valve guide remover (ø5)
90890-04097
Valve guide remover (5.0 mm)
YM-04097
Valve guide installer (ø5)
90890-04098
Valve guide installer (5.0 mm)
YM-04098
Valve guide reamer (ø5)
90890-04099
Valve guide reamer (5.0 mm)
YM-04099
Exhaust
Valve guide remover (ø4.5)
90890-04116
Valve guide remover (4.5 mm)
YM-04116
Valve guide installer (ø4.5)
90890-04117
Valve guide installer (4.5 mm)
YM-04117
Valve guide reamer (ø4.5)
90890-04118
Valve guide reamer (4.5 mm)
YM-04118
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 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
0.020 mm (0.0008 in)
VALVES AND VALVE SPRINGS
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 limit (in-
take)
1.6 mm (0.06 in)
Valve seat contact width limit (ex-
haust)
1.6 mm (0.06 in)
a. Apply blue layout fluid "b" onto the valve
face.
b. Install the valve into the cylinder head.
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