2004 SR Johnson 2 Stroke 9.9, 15, 25, 30 HP Outboards Service Manual, Page 196Get this manual
POWERHEAD INSPECTION
9.915 Models
The difference between your measurements and standard bore dimension is cylinder oversizeRefer to TECHNICAL DATA on p30 for dimensions The cylinder must not be oversize by more than 0.002 in(0.05 mm)
Use feeler gauge to check groove side clearance on the lower square ringsInstall each square ring on its pistonWith the ring seated in its groove, make several checks around the pistonThe side clearance must not exceed 0.004 in(0.10 mm)
IMPORTANT: If any cylinder is outside these tolerances, it must be bored oversizeOne oversize piston is available for this engine 0.020 in(0.508 mm)To determine oversize bore, add 0.020 in(0.508 mm) to the standard boreRefer to TECHNICAL DATA on p30It is permissible to have one or more oversize pistons in an engineMeasure the piston in two locations, 90 apart from each other, 18 in(3 mm) above the bottom of the piston skirt The difference between the two measurements is the out-of-roundness and must be no more than 0.002 in(0.05 mm)