Yamaha F2.5C, Service Manual, Page: 89 / 184

6D55F11
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7. If the valve seat contact area is too nar-
row and situated near the top edge of the
valve face, use a 30° cutter to cut the top
edge of the valve seat. If necessary, use
a 45° cutter to center the area and set its
width.
b
Previous contact width
8. If the valve seat contact area is too nar-
row and situated near the bottom edge of
the valve face, use a 60° cutter to cut the
bottom edge of the valve seat. If neces-
sary, use a 45° cutter to center the area
and set its width.
b
Previous contact width
9. Apply a thin, even layer of lapping com-
pound onto the valve seat, and then lap
the valve using a valve lapper (commer-
cially available).
CAUTION:
Do not get the lapping compound on the
valve stem and valve guide.
10. After every lapping procedure, be sure to
clean off any remaining lapping com-
pound from the cylinder head and the
valve.
11. Check the valve seat contact area of the
valve again.
Checking the rocker arms and rocker
arm shaft
1. Check the rocker arms, rocker arm shaft,
and rocker arm contact surface
a
for
wear. Replace if necessary.
2. Measure the rocker arm inside diameter
b
and rocker arm shaft outside diameter
c
. Replace if out of specification.
Rocker arm inside diameter
b
:
16.000–16.018 mm
(0.6299–0.6306 in)
Rocker arm shaft outside
diameter
c
:
15.971–15.991 mm
(0.6288–0.6296 in)
Cylinder head