1990 Johnson Evinrude "ES" 9.9 thru 30 Service Manual, P/N 507871, Page 143Get this manual
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 Engine Specifications, Section 1It is permissible to have one or more oversize pistons in an engine 1201 9Measure the mm) above thelocations,of90 apart from each piston in two other, Va in(3 bottom the piston skirt10The difference between the two measurements is the outof-roundness and must be no more than 0.002 in (0,05 mm)11 Refer to Engine Specificationsin Section for piston dimensions