the cylinder towards and away from each other in compression and power strokes, said pistons covering these ports during most of their strokes and suc- [52] US. 123/18 R F02B 53/00; F02B 55/00 cessively opening the ports as the pistons approach the Int. [51] ends of their respective power strokes, a pair of crank Fleld 0f R, A h f including intermeshing g and a p of necting rods connecting the cra