Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 139Get this manual
Condition: The valve seat is centered on valve face but it is too wide Condition: Valve seat is too narrow and it is near va lve margin55801
, :.7Va lve Seat Cutter Set Use 15 Cutter 60 Cutter
Desired Resu lts To reduce valve seat width Valve Seat Cutter Set Use 15 Cutter, First 45 Cutter Desired Results To center the seat and to achieve its Width
Lightly
Condition: The valve seat is in the middle of the valve face but it is too narrow55800