1974 Johnson 40 HP Outboard Motors Service manual, Page 49Get this manual
Check cylinder for size and wall straightness by using an inside micrometer or dial bore indicator Refer Secti on (or specified dimensionsReplace cylInder block, or rebare block for oversize pistons if wear is in excess of ,003", Pistons and ring sets are available .030" oversize,
If your shop is not equippea to rebare cylinder blocks, write our Service Department about our reboring service
Carbon ccumulation in the exhaust ports estricts the Clow of exhaust gases andhas considerable effect on performance of the motorCarefully scrape ca rbon from cylinder heads and exhaust ports with scraper or other blunt Instrument Exhaust ports and all exhaust passages must be free from carbon deposits to insure maximum performance, Figure 5-15 "LOOSE" Mark on Piston
DO NOT scratch cy linder head gasket surface of cylinderUse surface plate to sw-lace this area, With 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 cylinde wallsThe result will be reduced compresSion nd decrease in performance of the engineBefore reinstalling the pistonsbreak the glaze by using Cine cylinder hone to refinish cylinder walls ew up and down motions of the tool should be suffi cient to remove cylinder wall glazeSee Figure 5-17Blow out all oil passages and drains