Checking The Valve Guides; Replacing The Valve Guides - Yamaha F25C Service Manual

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Checking the valve guides

NOTE:
Before checking the valve guide make sure
that the valve stem diameter is within specifi-
cation.
1. Measure the valve guide inside diameter
a.
Valve guide inside diameter a:
Intake and exhaust:
5.500–5.512 mm
(0.2165–0.2170 in)
2. Calculate the valve stem-to-valve guide
clearance as follows. Replace the valve
guide if out of specification.
Valve stem-to-valve guide clearance
= valve guide inside diameter – valve
stem diameter:
Intake and exhaust:
0.025–0.052 mm
(0.0010–0.0020 in)

Replacing the valve guides

1. Remove the valve guide 1 by striking
the special service tool from the combus-
tion chamber side.
5-25
Power unit
Valve guide remover/installer:
90890-06801
2. Install a new valve guide 2 by striking
the special service tool from the cam-
shaft side until the valve guide clip 3
contacts the cylinder head.
NOTE:
Apply engine oil to the surface of the new
valve guide.
Valve guide remover/installer:
90890-06801
3. Insert the special service tool into the
valve guide 2, and then ream the valve
guide.
NOTE:
• Turn the valve guide reamer clockwise to
ream the valve guide.
• Do not turn the reamer counterclockwise
when removing the reamer.
Valve guide reamer: 90890-06804
6D55F11