1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 171Get this manual
INote Ilf any cylinder is outside these tolerances, it must be bored oversize 0.030 in(0,762 mm) oversize piston is available for this engineTo determine oversize bore add 0.030 in(0,762 mm) to the standard boreRefer to Engine Specifications, Section 1It is permissible to have one or more oversize pistons in an engine
1271 9Use micrometer to measure the piston major diameter 18 in(3,2 mm) above the bottom edge of the piston skirtThe micrometer should be in line with the upper piston ring dowel pin The major diameter should be no smaller than 3.1831 in(80,85 mm) for standard piston and 3.2131 in(81,61 mm) for an oversize piston
10Measure the piston in several more locations 18 in(3,2 mm) above the bottom edge of the piston skirtNo measurement should be larger than the major diameter and no measurement should be more than 0.004 in(0,10 mm) smaller than the major diameter1281 If the grooves on the sides of the piston are worn smooth in an area similar to that shown, replace the piston