Yamaha MTN850-A 2017 Service Manual page 259

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 (intake)
0.010–0.037 mm (0.0004–0.0015
in)
Limit
0.080 mm (0.0032 in)
Valve-stem-to-valve-guide clear-
ance (exhaust)
0.025–0.052 mm (0.0010–0.0020
in)
Limit
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
head to 100 C (212 F) in an oven.
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a. Remove the valve guide with the valve guide
remover "1".
VALVES AND VALVE SPRINGS
b. Install the new valve guide with the valve
guide installer "2" and valve guide remover
"1".
Valve guide position
13.3–13.7 mm (0.52–0.54 in)
a. Valve guide position
c. After installing the valve guide, bore the valve
guide with the valve guide reamer "3" to ob-
tain the proper valve-stem-to-valve-guide
clearance.
TIP
After replacing the valve guide, reface the valve
seat.
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