2004 SR Johnson 2 Stroke 9.9, 15, 25, 30 HP Outboards Service Manual, Page 197Get this manual
POWERHEAD INSPECTION
2530 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 0.003 in(0.08 mm)
The minor diameter must be smaller than the major diameter by the cam dimensionSee Piston Dimension Chart
IMPORTANT: If any cylinder is outside these tolerances, it must be bored oversizeOne oversize piston is available for this engine 0.030 in(0.762 mm)To determine oversize bore, add 0.030 in(0.762 mm) to the standard boreRefer to TECHNICAL DATA on p.30It is permissible to have one or more oversize pistons in an engineMeasure the piston diameter in at least two places to check piston condition Make your measurements 18 to 14 in(3.2 to 6.4 mm) above the bottom edge of the piston skirt