Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 114Get 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 instructionsMeasure valve seat width (a)Resuriace the valve seat if not in specification
Valve Seat Width Specificationa" Standard Value Intake Valve Seat Exhaust Valve Seat