1978 Johnson 55 HP Outboards Service Manual, Page 59Get this manual
then down and out the exhaust ports on the adjacent side of the cylinder wallThe flow pattern of the incoming fresh fuel laden gases very effectively "drive" the burned exhaust gases from the cylinderThis results in clean and powerful "charge" ready to be compressed and burned as the piston reaches the top of its strokeSee Figures 5-3 and 5-4Windows in the piston of this loop scavenged engine allow the fuel mixture to enter the cylinder from the crankcase through smooth unbroken transfer passage, correctly designed for best efficiencyCRANKCASE AND CYLINDERS split crankcase and cylinder assembly Simplifies power head servicingThe cylinder heads are combined in one castingPISTONS The pistons, with the piston rings, receive the force of combustion in the cylinder head, so it is necessary that both the pistons and piston rings be properly fitted to form seal between the piston head and cylinder wallsTo retain maximum power within the cylinder above the piston head, the cylinder must be perfectly round and the piston rings correctly seated in their grooves681223 6812.24