Internal combustion engine

Internal combustion engine comprises a cylinder crank case (10) containing two working cylinders in which working pistons (18, 20) connected to cranks (32, 34) of a crank shaft (36) oscillate in phase with each other. The crank case contains three cylinders (12, 14, 16) having identical dimensions and arranged in a row. The outer cylinders (12, 16) are the working cylinders. An equalizing weight (40) oscillates in the middle cylinder out of phase with the working pistons. Preferred Features: The equalizing weight is a piston geometrically designed so that it oscillates in the middle cylinder without performing any compression work.