1992 Johnson Evinrude "EN" 9.9 thru 30 Service Manual, P/N 508142, Page 186Get this manual
1411 9Measure the piston diameter in at least two places to verify piston conditionMake your measurements 18 to 114 in(3,2 to 6,4 mm) above the bottom edge of the piston skirt
rN=J These engines have pistons of several different manufacturersUse the chart below to visually identify the piston you are measuring and select the appropriate dimensions The major diameter of the piston is measured 90 from the wrist pin hole centerline See the chart The minor diameter of the piston is measured in line with the wrist pin hole centerlineThe minor diameter must be smaller than the major diameter by the cam dimensionSee the chart