1980 Johnson 4HP Service Manual, Page 52Get this manual
Since the pistons, with the piston rings, receive the force of combustion in the cylinder head, it is necessary that both the pistons and piston rings properly fitted to form seal between the piston head and cylinder wallsretain maximum power within the cylinder head, the cylinder must perfectly round and the piston rings correctly seated in their groovesCONNECTING RODS, CRANKSHAFT, AND BEARINGS The connecting rods provide linkage between the piston and crankshaftThe force of
bustion, applied to the piston in reciprocating straight line thrust, is converted to rotating power at the crankshaft through the linkage of the connecting rodThe crankshaft is of the two-throw type and is supported two cast-in upper needle bearing main bearings and COOLING SYSTEM The powerhead is water cooledwater pump, the driveshaft, forces water through driven channels in the powerheadHeated water is discharged through the exhaust tube