Checking The Valves And Valve Guides - Yamaha YZ250FXM 2021 Owner's Service Manual

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EAM30091
CHECKING THE VALVES AND VALVE
GUIDES
1. Measure:
• Valve-stem-to-valve-guide clearance
Out of specification  Replace the valve
guide.
Valve-stem-to-valve-guide clearance =
Valve guide inside diameter "a" -
Valve stem diameter "b"
Valve-stem-to-valve-guide clear-
ance limit (intake)
0.080 mm (0.0032 in)
Valve-stem-to-valve-guide clear-
ance limit (exhaust)
0.100 mm (0.0039 in)
2. Replace:
• Valve guide
TIP
To ease valve guide removal and installation,
and to maintain the correct fit, heat the cylinder
VALVES AND VALVE SPRINGS
head to 100 °C (212 °F) in an oven.
a. Remove the valve guide with the valve
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b. Install the new valve guide with the valve
c. After installing the valve guide, expand the
TIP
After replacing the valve guide, reface the valve
seat.
5-28
guide remover "1".
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guide installer "1" and the valve guide re-
mover "2".
Valve guide installation height "a"
Intake
10.8–11.2 mm (0.43–0.44 in)
Exhaust
11.2–11.6 mm (0.44–0.46 in)
2 2 2
1 1
hole in the valve guide with the valve guide
reamer "3" to obtain the proper valve-
stem-to-valve-guide clearance.