Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 157Get this manual
7Remove crankshaft from block8Remove balance rod and main bearings Inspection
Cylinder Bore
MEASURING CYLINDER BORE 1Measure the cylinder bore diameter at three locations in both and axis2If the cyl inder bore is beyond the standard limits listed in the tables below, it wi ll be necessary to re-bore the cylinder to accept the oversize piston
NOTE: Do not interchange main bearings, re -install in there original locations9Remove oil seals
aOil SealsBalance RodMain Bearings
Piston Disassembly