Yamaha YZ 2019 Series, Owner'S Service Manual

Page: 224 / 398

VALVES AND VALVE SPRINGS
5-25
c. After installing the valve guide, expand the
hole in the valve guide with the valve guide
reamer “3” to obtain the proper valve-stem-
to-valve-guide clearance.
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 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.
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
Valve stem runout
0.010 mm (0.0004 in)
Valve seat contact width (intake)
0.90–1.10 mm (0.0354–0.0433 in)
Limit
1.6 mm (0.06 in)
Valve seat contact width (ex-
haust)
0.90–1.10 mm (0.0354–0.0433 in)
Limit
1.6 mm (0.06 in)