Yamaha F90D - Refacing the Valve Seat

6D81G11
5-30
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Refacing the valve seat
1. Reface the valve seat with the valve seat
cutters.
2. Cut the surface of the valve seat with a
45° cutter by turning the cutter clockwise
until the valve seat face has become
smooth.
a
Slag or rough surface
CAUTION:
Do not over cut the valve seat. Be sure to
turn the cutter evenly downward at a pres-
sure of 40–50 N (4–5 kgf, 8.8–11 lbf) to
prevent chatter marks.
3. Use a 30° cutter to adjust the contact
width of the top edge of the valve seat.
b
Previous contact width
4. Use a 60° cutter to adjust the contact
width of the bottom edge of the valve
seat.
b
Previous contact width
Valve seat contact width
a
:
1.20–1.60 mm (0.0472–0.0630 in)
Neway valve seat kit: YB-91044
S69J5845
30˚
45˚
30˚
45˚
60˚
S63P5230
S69J5880
30˚
b
S69J5890
60˚
b
Cylinder head