1972 Johnson 4HP Outboard Motor Service Manual, Page 40Get this manual
Figure 5-9Removing Retaining Rings Figure 5-11"L" Mark Piston
CLEANING, INSPECTION, AND REPAIR
CYLINDER BLOCK AND Check cylinder walls for excessive wear and check cylinder ports for carbon accumulationCylinder walls wear in various degrees depending lubri cation and conditions under which the motor is
operatedMajor portion of wear is in the port area and the area covered ring travelCheck cylinder for size and wall straightness using an inside micrometer or dial bore indicatorRefer to Section for specified dimensionsIf wear is greater than .002", replace cylinder block or rebore block for oversize pistonsPiston and ring sets are available .030" oversize[jJNOTE If your shop is not equipped to inder blocks, write the Factory Service Department about our serviceCarbon accumulation in the exhaust ports restricts the f10w of exhaust gases and has considerable effect performance of the motorCarefuHy scrape carbon from cylinder heads and exhaust ports with scraper or other blunt instrumentExhaust ports and exhaust passages must free from carbon deposits to insure maximum performanceWith continued operation of the motor, the cylinder walls will take glaze which reduces the effectiveness of the seal between the piston rings and reduced the cylinder wallsThe result will compression and decrease in performance of the engineBefore reinstalling the pistons, break the glaze using fine cylinder honefew up and down motions of the tool in the cylinders should sufficient to remove the glazeSee Figure 5-12GASKET SURFACES Remove traces of dried cement from gasket surfaces, using trichlorethyleneCheck gasket faces for flatnessUnder certain conditions, gasket faces warp or spring, particularly where thin tions or flanges are employed and are subject to temperature changes2014