Abstract: This invention relates to internal combustion engines, the energy output of which is produced as hydraulic pressure, and in one embodiment comprises two, two-cycle internal combustion engines which face each other, the piston rods of each of which are axially aligned and are linked to both of the axially aligned drive pistons of two hydraulic pumps which also face each other by means of four connecting rods of equal length, the axis of the pump rods being at right angles to that of the engine rods, and associated hydraulic circuitry which includes means for selectively initiating the compression phase of the engines when their respective pistons have thrust outward toward each other to such an extent that the angle between the axis of each of said piston rods and its associated connecting rods has passed through a right angle and said rods would otherwise be retained in said extended position through force exerted on said connecting rods by the pistons of the hydraulic pumps.