1975 Evinrude 40 HP Outboards Service Manual, PN 5093, Page 52Get this manual
Figure 5-19ACleaning Carbon From Lower Ring Groove
Figure 5-22Checking Fit of Ring in Groove
Figure 5-20Checking Piston Skirts for Roundness
Figure 5-23Checking Groove Side Clearance damaging the rooveA tool for cleaning ring grooves can be made by breaking an old ring, grinding an angle on the edge, and breaking the lower sharp edge to prevent damage to lower ring landSee Figure 5-19ACheck piston for size and roundness, using micrometerSee Figure 5-20 Piston skirt must be perfectly round and not scratchedCorrect sizes are given in Section 2Before installing new piston ringscheck gap between ends of ring by placing ring in its respective cylinder bore, then pushing the ring down in the bore slightly with the bottom of the piston to square it up Discard and replace with new ring if gap is excessiveSee Figure 5-21 Check each ring in its respective ring groove for evidence of tightness or binding by rolling the ring around the piston ring grooveSee Figure 5-22Check for groove side clearance with feeler gage See Figure 5-23Correct gap and side clearances are given in Section 25-9