Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 121Get this manual
64Remove seali ng rings with ring remova tool (91 24697) NOTE: EYE PR OTECTION MUST BE USED when removing sealing rings
1Thoroughly clean cyl inder block and crankcase coverBe sure that aU sea lant and ld gaskets are removed from matching surfcesBe sure that carbon deposits are removed from exhaust ports2Inspect cylinder block and crankcase cover for cracks or fractures3Check gasket surfaces for nicks, deep grooves, cracks and di storti on that could cause compression leakages4Check aU water and oit passages in cylinder block and crankcase cover to be sure that they are not obstructed and that plugs are in place and tight