1968 Evinrude Ski-Twin, Ski-Twin Electric 33 HP Outboards Service Manual, Page 46Get this manual
grinding an angle the edge, and breaking the lower sharp edge to prevent damage to lower ring landSee Figure 5-17Check piston for size and roundness, using micrometerSee Figure 5-18Piston skirt must perfectly round and not scratchedCorrect sizes given in Section 2Before instaHing new piston rings, check gap between ends of ring placing ring in its respective cylinder then pushing the ring down in the slightly with the bottom of the piston to square it Discard and replace with new ring if gap is excessiveSee Figure 5-19Check each ring in its respective ring groove for evidence of tightness binding rol1ing the ring around the piston ring grooveSee Figure 5-20Check for groove side clearance with feeler gage See Figure 5-21Correct gap and side clearances given in Section 2Figure 5-19Checking Ring Gap in Cylinder