Abstract: The invention consists of a two-stroke opposing cylinder engine that includes a length flushing system and two crankshafts (1, 3) and a novel type of phase setting mechanism which enables the compression ratio to be adjusted in operation. Two intermediate gear wheel (15) and (16) synchronize rotation of the crankshafts (1, 3). The centre positions of the two intermediate gear wheels (15, 16) are moved by means of a setting device (21) so as to change the phase position between the crank shafts (1, 3) and therewith the compression. With the aid of the two intermediate gear wheels (15, 16) the crankshafts will rotate in mutually opposite directions, therewith eliminating torque-dependent vibrations.