Checking The Cylinder Head - Yamaha F2.5A Service Manual

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 obtainable).
69M3E11
CAUTION:
Do not get the lapping compound on the
valve stem or 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 cylinder head

1. Eliminate carbon deposits from the com-
bustion chambers and check for deterio-
ration.
2. Check the cylinder head warpage using a
straightedge 1 and thickness gauge 2
in six directions as shown. Replace if out
of specification.
S69M5390
1
Cylinder head warpage limit:
0.1 mm (0.004 in)
Cylinder head
1
2
3
4
5
2
6
S69M5420
7
8
S69M5430
9
5-20