2001 Mercury Mariner 50-60HP Factory Service Manual, Page 231Get this manual
CYLINDER HEAD
Valve Refacing Steps
Condition: The valve seat is centered on valve face but it is too wide
Valve Seat Cutter Set Use Lightly Li htl 15 Cutter 60 Cutter
Desired Results To reduce valve seat width
Condition: The valve seat is in the middle of the valve face but it is too narrow
Valve Seat Cutter Set Use 45 Cutter