2001 Mercury Mariner 50-60HP Factory Service Manual, Page 230Get this manual
CYLINDER HEAD
Valve Seat Reconditioning
Clean the carbon deposits from the combustion chambers and valve seats and check for pittingSeveral different types of equipment are available for reseating valve seatsFollow the equipment manufacturer's instructionsReface valve seat; use 60, 45, 15 valve seat cutterMeasure valve seat width (a)Resurface the valve seat If not in specification