2003 Johnson ST 6/8 HP 4 Stroke Outboards Service Manual, PN 5005471, Page 146Get this manual
POWERHEAD INSPECTION If the grinding on the sides of the piston is worn smooth in pattern similar to the following illustration, replace the pistonseveral checks around the pistonThe side clearance must not exceed 0.004 in(0.10 mm)
Place each ring, separately, in its respective cylinder boreUse piston to square the ring in the cylinderUse feeler gauge to measure the ring end gapThe ring gap must be within 0.006 to 0.014 in(0.15 to 0.35 mm)
Use machinist's straightedge to check clearance on the top two ringsInstall each ring 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 groove