Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 238Get this manual
Pistons and Piston Rings IMPORTANT: If engine was submerged while engine was running, piston pin andor connecting rod may be bentIf piston pin is bent, piston must be replaced(Piston pins are not sold separately because of matched fit into piston If piston pin is bent, connecting rod must be checked for straightness (refer to "Connecting Rods," following, for checking straightness)1Inspect pistons for scoring and excessive piston skirt wear2Check tightness of piston ring locating pinsLocating pins must be tight3Thoroughly clean pistonsCarefully remove carbon deposits from pistons, with soft wire brush or carbon remove solutionDo not burr or round off machined edgesInspect piston ring grooves for wear and carbon accumulationIf necessary, scrape carbon from piston ring grooves being careful not to scratch sides of groovesRefer to procedure following for cleaning piston ring groovesCLEANING PISTON RING GROOVES Keystone (tapered) ring grooves
MEASURING PISTON ROUNDNESS Piston has barrel profile shape and is not true diameter1Using micrometer, measure dimension "A" at location shownDimension "A" should be as indicated in chart followingPiston Standard Piston .015 inOversize Piston .030 inOversize Piston Dimension "A" 3.6210 in .0005 in3.636 in .0005 in4.383 in .0005 in