1978 Evinrude Outboards 9.9/15HP Service Manual, Page 64Get this manual
WORN RING GROOVES
BREAK THIS EDGE
CARBON ED RING AND GROOVE
Figure 5-26Cleaning Carbon from Ring Groves
REFERENCE PICTURE
SERVICEABLE RING SQUARE EDGE
Figure 5-25Piston and Ring Condition Lower and upper crankcase seal and "0" ring should be replacedf