Yamaha F40BMHD Manuel D'entretien page 238

POWR
C
B
A
A
B
C
D
CYLINDER HEAD
Valve seat cutter set
YM-91043-C/90890-06803
Cut section as follows
Section
A
B
C
Refacement steps
Valve seat is centered on valve face but
A
is too wide.
Valve seat cutter set
90° cutter
Use
lightly
30° cutter
Valve seat is in the middle of the valve
B
face but is too narrow.
Valve seat cutter set
Use 45° cutter
Valve seat is too narrow and is near
C
valve margin.
Valve seat cutter set
90° cutter
Use
45° cutter
Valve seat is too narrow and it is
D
located near the bottom edge of the
valve face.
Valve seat cutter set
30° cutter
Use
45° cutter
5-35
E
Cutter
90°
45°
30°
Desired result
To reduce valve seat
width.
Desired result
To achieve a uniform
valve seat width.
Desired result
To center the seat
and set its width.
Desired result
To center the seat
and increase its
width.