Abstract: An internal combustion engine (1) comprising at least two cylinders (4,8) meeting to form a combustion space (12) therebetween, a first piston (3) adapted to reciprocate within the first cylinder (4) and a second piston (7) adapted to reciprocate within the second cylinder (8). The two pistons are drivably coupled via a chain drive connecting their respective crankshafts and synchronously move one with respect to the other such that the second piston moves at a frequency haft of that of the first piston. An air/fuel mixture inlet aperture (14) as well as an exhaust aperture (15) are located in the wall of the second cylinder (8) and are opened or closed by the movement of the second piston (7).