Yamaha F100B F100C Outboards Factory Service Manual, Page 123Get this manual
Cylinder head CAUTION:
Do not over cut the valve seatBe sure to turn the cutter evenly downward at pressure of 4050 (45 kgf, 8.811 lbf) to prevent chatter marks3Use 30 cutter to adjust the contact width of the top edge of the valve seat6If the valve seat contact area is too wide and situated in the center of the valve face, use 30 cutter to cut the top edge of the valve seat, 60 cutter to cut the bottom edge to center the area and set its width
b Previous contact width
S60C5560
b Previous contact width
4Use 60 cutter to adjust the contact width of the bottom edge of the valve seat