Valve Seat Refacing; Valve Seat Cutting Guidelines - Yamaha F20A Service Manual

POWR
Å
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CAMSHAFT AND VALVES

Valve seat refacing

NOTE:
After refacing the valve seat or replacing
the valve and valve guide, lap the valve seat
and valve face.
CAUTION:
To prevent chatter marks, turn the valve
seat cutter while applying an even, down-
ward pressure (4 ~ 5 kg).
Valve seat cutter set:
YM-91043-C/90890-06803
Refer to the following chart to deter-
mine the appropriate valve seat cut-
ter.
Valve seat area
A
B
C

Valve seat cutting guidelines

Å The valve seat is centered on the valve face,
but is too wide.
Valve seat cutter set
First:
Use 90˚ cutter
lightly Second:
30˚ cutter
ı The valve seat is in the middle of the valve
face, but is too narrow.
Valve seat cutter set
Use 45˚ cutter
5-28
E
Valve seat cutter
90˚
45˚
30˚
Desired result
To reduce the
valve seat width.
Desired result
To achieve a
uniform valve seat
width.