Abstract: An internal combustion engine is provided. The engine includes a housing (9) having at least first and second pairs of chambers (20) formed in the housing. Each chamber extends from the exterior of the housing to a predetermined point therein. The first pair of chambers being aligned with the housing along a first axis and the second pair of chambers being aligned within the housing along a second axis extending substantially normal to the first axis. The engine further including a plurality of piston assemblies (6). Each chamber having one of the piston assemblies rigidly fastened thereto. A cylinder (1) is reciprocally mounted on an elongate cylinder pin assembly (2). The cylinder pin assembly extending within the housing and disposed between the cylinders for reciprocating the cylinders along a predetermined stroke length and relative to the fixed piston assemblies in an opposed manner during operation of the engine. The cylinder pin assembly having two axes of rotation.