Yamaha F25A, Service Manual

Page: 162 / 444

5-24
POWR
E
CAMSHAFT AND VALVES
SERVICE POINTS
Valve inspection
1. Measure:
●
Valve guide bore
a
Out of specification
→
Replace the
valve guide.
2. Measure:
●
Valve seat width
a
Out of specification
→
Reface the
valve seat.
Valve guide bore limit:
5.500 ~ 5.512 mm
(0.2165 ~ 0.2170 in)
Valve seat width limit:
0.9 ~ 1.1 mm (0.035 ~ 0.043 in)
3. Measure:
●
Margin thickness
a
Out of specification
→
Replace the
valve.
Margin thickness:
IN: 0.6 ~ 1.0 mm
(0.024 ~ 0.039 in)
EX: 0.7 ~ 1.1 mm
(0.028 ~ 0.043 in)
4. Measure:
●
Valve stem diameter
a
Out of specification
→
Replace the
valve.
Valve stem diameter:
IN: 5.475 ~ 5.490 mm
(0.2155 ~ 0.2161 in)
EX: 5.460 ~ 5.475 mm
(0.2150 ~ 0.2155 in)