1985 OMC 65, 100 and 155 HP Models Commercial Service Manual, PN 507450-D, Page 189Get this manual
Pistons Check the pistons for roundness, excessive skirt wear, and scoringCarefully remove carbon deposits from inside piston headInspect the ring grooves for carbon accumulation, excessive wear, or damage to the ring seatsPistons should be marked before they are removed and returned to the same cylinder if reusedCarefully scrape carbon from the ring grooves, making certain that carbon cl inging to the bottom and sides of the grooves has been thoroughly removed without scratching or otherwise damaging the groovesA tool for cleaning ring grooves can be made by breaking an old ring, grinding the edge, and breaking the lower sharp edgeDO NOT damage the lower ring landCheck piston for size and roundness, using micrometerBefore installing new piston rings, check gap between ends of ring by placing ring on its respective cylinder bore, then pushing the ring down in the bore slightly with the bottom of the piston to square it upDiscard and replace with new ring if gap is excessiveCheck each ring in its respective ring groove for evidence of tightness or binding by rolling the ring around the piston ring grooveCheck for groove side clearance with feeler gageCorrect gap and side clearances are given in Section 1Oil Seals Use the parts book for reference to position seals for installation ]:;",