Honda BF8, BF9.9 and BF10 Outboard Motors Shop Manual., Page 171Get this manual
2) Use the 32' and 60' cutter to narrow and adjust the valve seat so that it contacts the middle of the valve face The 3' cutter removes material from the top edge2 The 60' cutter removes material from the bottom edge,
3) Be sure that the width of the finished valve seat is within specification
Standard valve seat width
0.9mm (0.0350.043 in)
4) Make light pass with 45' cutter remove any possible
burrs at the edges of the seat5) After resurfacing the seats, inspect for even valve seat-