2004 SR Johnson 2 Stroke 9.9, 15, 25, 30 HP Outboards Service Manual, Page 198Get this manual
POWERHEAD INSPECTION Place each ring, in turn, in its respective boreUse piston to square the ring in the cylinderUse feeler gauge to measure the ring end gapThe ring gap must be within 0.007 to 0.017 in(0.17 to 0.43 mm)Use machinist's straightedge to check clearance on the upper Pressure-BackTM ringsInstall each Pressure-Back ring on its pistonRing to piston clearance should allow the straightedge to touch the piston on both sides of the ring grooveSee imageMake several checks around the pistonIf the straightedge does not touch the piston, remove the ring and clean the ring groove