1995 Johnson/Evinrude Outboards 9.9, 15 four-stroke Service Manual, Page 117Get this manual
16Place the top two rings of each piston, separately, in its respective boreUse piston to square the ring in the cylinderUse feeler gauge to measure the ring end gap The ring gap (O,15-0,51 mm)must be within 0.006-0.020 in
17Use feeler gauge to check groove side clearance on the top two ringsInstall rings on pistonWith the ring seated in its groove, make several checks around the pistonThe side clearance must not exceed 0.004 in(O,10 mm)
18Use machinist's straightedge to check clearance on the top two ringsInstall rings on its pistonWhen checked with the straightedge, there should be enough ring clearance to allow the straightedge to touch the piston on both sides of the ring grooveMake several checks around the pistonIf straightedge does not touch piston, remove the ring and clean ring groove19If the grinding on the sides of the piston is worn smooth in pattern similar to the illustration, replace the piston