Tohatsu 4 Stroke MFS 2/2.5/3.5A Outboards Service Manual, Page 102Get this manual
5 Use 45 degree cutter to adjust contact width of valve seat to specified value
b Width before correction Specified width
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 wide30
b Width before correction
If valve seat contact area is narrow and is located nearer to valve face upper end, use 30 degree seat cutter to cut upper endIf necessary, use 45 degree cutter to adjust contact width of valve seat to specified value30