Yamaha WR450F 2021, Owner'S Service Manual, Page: 230 / 402

VALVES AND VALVE SPRINGS
5-28
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.
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.
a. Apply blue layout fluid “b” onto the valve
face.
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide
and onto the valve seat to make a clear
impression.
d. Measure the valve seat contact width “c”.
TIP
Where the valve seat and the valve face are in
contact with each other, the blueing will have
been removed.
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
Valve stem runout
0.020 mm (0.0008 in)
Valve seat contact width limit (in-
take)
1.5 mm (0.06 in)
Valve seat contact width limit (ex-
haust)
1.5 mm (0.06 in)