1995 Mariner Mercury Outboards Service Manual 50HP 4-Stroke, Page 129Get this manual
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 instructionsMeasure valve seat width (a)Resurface the valve seat If not in specification
Valve Refacing Steps
ConditionThe valve seat is centered on valve face but it is too wide
Valve Seat Cutter Set
Desired Results
Use Lightly
15 Cutter 60 Cutter
To reduce valve seat width
Valve Seat Width Specification "a "