Yamaha Marine Outboards F4A/F4 Factory Service Manual, Page 162Get this manual
ROCKER ARM AND VALVES
Valve seat refacing
After refacing the valve seat or replacing the valve and valve guide, lap the valve seat and valve face
To prevent chatter marks, turn the valve seat cutter with an even, downward pressure (4kg)Valve seat cutter set: YM-91043-C90890-06803 Valve seat lapper: N.A90890-06805
9Refer to the following chart to deter-
mine the appropriate valve seat cutterValve seat area Valve cutter 45 60