1976 Johnson 4HP 4R76, 4W76 Outboards Service Manual, Page 42Get this manual
ONaTE DO NOT scratch cylinder head gasket surfac of cylinderUse surface plate to surface this area
PISTONS Check the pistons for roundness, excessive shirt wearand scoringThe piston skirts must be perfectly round and unscratched to prevent the entry of exhaust gases into the crankcase chamberCarefully remove carbon deposits from inside piston headInspect the ring grooves for carbon accumulationexcessive wear, or damage to the ring groovesCarefully scrape carbon from the ring grooves, making rtain that carbon clinging to the bottom and sides of the groove has been thoroughly removed without cratching or otherwise damaging the groovesA tool for cleaning the ring grooves can be made from broken ring with sharpened edge Care must be taken not to damage the ring landsSee Figure 5-14Clean carbon from top of pistontaking care not to alter piston deflectorCheck piston for size and roundnessusing micrometerCorrect sizes are given in Section 2