TOHATSU MFS25 Service Manual page 152

Power Unit
Use 45 degree cutter to adjust contact width of valve seat c
5.
to specified value.
6. Valve seat contact area is located on the center, which
should be adjusted to specified value by cutting upper and
lower ends by using 30 degree and 60 degree seat cutters
respectively if the area is too wide.
7. If valve seat contact area is too narrow and is located neater
to valve face upper end, use 30 degree seat cutter to cut
upper end. Use 45 degree cutter to adjust contact width of
valve seat to specified value.
8. If valve seat contact area is too narrow and is located neater
to valve face lower end, use 60 degree seat cutter to cut
lower end. Use 45 degree cutter to adjust contact width of
valve seat to specified value.
5-36
b Width before correction
c Specified width
30˚
b
60˚
b Width before correction
b
30˚
b Width before correction
b
60˚
b Width before correction
b
c
45˚
25/30 2006