1978 Evinrude Outboards 9.9/15HP Service Manual, Page 63Get this manual
DO NOT scratch cylinder head gasket surface of cylinderUse surface plate to surface this areaWith continued operation of the motor, the cylinder walls will take on glaze which reduces the effectiveness of the seal between the piston rings and the cylinder wallsThe result will be reduced compression and decrease in performance of the motorBefore reinstalling the pistons, break the glaze by using fine cylinder hone to refinish cylinder wallsUse low rpm on drill with rapid up and down movement to obtain good crosshatch pattern for good oil retentionUse hone with medium stone (220 grit) REFERENCE PICTURE 433 6