1989 Johnson Evinrude "CE" 9.9 thru 30 Service Manual, P/N 507754, Page 147Get this manual
6 Check piston with micrometer to determine if piston has been distorted during assemblyMeasure the piston at two places, 90 from each other, Va to in(3,2 to 6,4 mm) above bottom edge of the skirtIf the difference between the two measurements is greater than
0.002 in(0,05 mm), the piston is out of round or worn and must
be replaced 7Install piston rings on each pistonSpread each ring with ring expander just enough to slip it over the head of the piston and down into place8Coat the pistons and cylinder bores with oil
9Place the piston in OMC Ring Compressor PI 326590 (for standard size piston)Make certain that the rings are correctly positioned in their grooves with respect to the dowel pinsDamaged pistons and broken rings may result from imperfect alignment of the ring gap and the dowel pins
INote pms piston ringspermanent correctly located on their dowel must be to prevent powerhead damage1321 10Start the piston into bore of the cylinder with deflector