Abstract: Reciprocating piston machine having a pair of spaced, parallel, double-ended cylinders straddling a crankshaft with a single crankpin. First and second double-ended pistons reciprocate within respective cylinders and are connected to crankshaft by T-shaped connecting member journalled on crosshead. Crosshead reciprocates on the crosshead guides positioned between and parallel to the cylinders. Connecting member has outer ends of piston connecting arms slidably and rotatably connected to pistons to accommodate changes in angle of connecting member, with outer end of crank connecting arm journalled on crankpin. Clearance openings extend between inner side walls of cylinder and crankcase to accept piston connecting arms, outer ends of openings serving as inlet ports. Exhaust ports are provided on generally opposite side of cylinder to inlet ports to permit efficient scavenging of spent charge.