[Brucelee]

Well-designed conventional reciprocating engines operating at conservative powers and speeds, irrespective of size or type, generally last about 5×108 revolutions before wear-out of the piston rings and the cylinder bore. Note that the engine life expectancy is a function of the number of revolutions rather than the total piston travel distance. Such a fact implies that wear-out is primarily due to the ring reversal event, i.e., the reversal in direction of ring travel that occurs twice each revolution. It is well known that maximum bore and ring wear occurs at ring reversal due to the "squeeze-out" of the oil film between the ring and bore when the ring is not moving.

Also, higher piston speed increases wear rates because of the increasing difficulty in maintaining an adequate oil film. It is generally accepted that average piston speed should not exceed about 2000 feet per minute, and low speed engines enjoy a life advantage over high speed engines.


As can be seen from FIG. 3, as engine speed increases, the frictional horsepower losses become quite significant in the conventional engine