Abstract: An opposed piston engine (10) comprising upper (12) and lower (14) cylinders and opposed pairs of pistons (16, 18) slidable therein and interconnected by rocker pivots (24, 26). A crankshaft (56) coupled to the rocker pivots (24, 26) constrains the movement of the pistons (16, 18) and is disposed with the crankshaft axis (58) intersecting the axis (44) of one of the cylinders (12, 14), whereby the geometry of the engine (10) is significantly changed thereby reducing torsional vibration and enabling a two stroke diesel version of the engine to be used as a power source for an aircraft propeller.