1997 Johnsoon Evinrude "EU" 50 thru 70 3-Cylinder Service Manual, P/N 507266, Page 155Get this manual
[] 9Use micrometer to check piston conditionMake at least two measurements, 90 from each otherMeasure the piston diameter in(6,4 mm) above the bottom edgeRefer to Engine Specifications, Section 1, for piston dimensions The difference between the two piston measurements must not exceed 0.003 in(0,08 mm)[] 10For new or used ring sets, make the following inspectionsPlace each ring, separately, in its respective boreUse piston to square the ring in the cylinderUse feeler gauge to measure the ring end gapThe ring end gap must be within: Recreational Models0.0190.031 in(0,480,79 mm) Commercial Models0.0100.022 in(0,250,56 mm)[11Use machinist's straightedge to check clearance on the tapered ringsInstall one tapered ring in the piston's upper ring grooveWhen checked with the straightedge, there should be enough ring clearance to allow the straightedge to touch the piston on both sides of the ring grooveMake several checks around the piston If straightedge does not touch piston, remove the ring and clean ring grooveRemove upper ring from pistonInstall remaining tapered ring in piston's lower ring groove and check for clearance !):::::.dr._