Mercury Mariner 8/9.9HP 4-Stroke Factory Service Manual, Page 131Get this manual
Valves 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 instructionsMeasure valve seat width (a)If not in specification, resurface the valve seat
Valve Refacing Steps
Condition: The valve seat is centered on valve face but it is too wide
Valve Seat Cutter Set Use Lightly Lightl 15 Cutter 60 Cutter
Desired Results To reduce valve seat width idth