2007-2009 Yamaha F15/F20 Outboard Service Manual, Page 132Get 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 seat
6Check the valve seat contact area of the valveNOTE: To check the valve seat contact area, see "Checking the valve seat" (5-41)7If 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 and 60 cutter to cut the bottom edge to center the area and set its width
S68V5750