Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 124Get this manual
Cleaning Piston Ring Grooves
Cylinder Heads and Exhaust Cover
1Thoroughly clean cylinder heads and gasket sur faces Remove carbon deposits and "varn ish" from cylinder heads (with fine wi re brush on shaft attached to an electric drill or use carbon remover solution) 2Inspect cylin der headsCheck for deep grooves, racks and distortion which cou ld cause compression leakage3Check spark plug holes for stripped or damaged threads4Inspect internal su rface of cylinder heads for possible dam age (as result of piston or foreign material striking cylinder heads)NOTE: Piston striking cyli nder head could be an ind icatio that connecting rod bearings (either end) are failing 5Replace cylinder head(s) as necessary6Th oroughly clean gasket surfaces of cylinder head coversCheck covers for deep grooves, racks and distortion that could cause water leakageReplace cover(s) as necessary7Thorough ly clean gasket su rfacs of exhaust manifold cover8inspect exhaust man ifold cover for deep grooves, racks distortion that coul cause leakageReplace parts as necessary