Abstract: A two-stoke cycle combustion-engine with crank-chamber compression is described, free of charging transfer passages external to the cylinder, with pumping-displacement exceeding working-displacement for responsive intake and thorough scavenging of spent-gas residue, and featuring an annular water-cooled cell, suspended from the cylinder-head by several water-conduits, and cooperating with an annular recess in the piston-head so as to form, and transversely separate, a plain working-chamber and an annular working-chamber, longitudinally scavengeable in series, bottom-to-top and top-to-bottom, respectively, with minimal loss of charge to exhaust-port, such a system of scavenging also reducing piston cooling-problems and misfiring associated with charge-dilution (in gasoline-engines operating under partial-charge conditions). In addition, a more general scavenging principle is enunciated and claimed, applicable to rear-compression and separately-scavenged two-stroke engines.