In a piston engine (1) with piston/cylinder units (2 to 5) arranged in a row, a cam body (14) with diametrically opposed cams (15 and 16) is secured to a crankshaft (10) in a central transversal plane (13). A balancing mass (19) lies with a cam roll (18) on the cam body (14). The cam roll (18) is constantly held against the cam body (14) by a compression spring (17) fixed to the engine. The cams (15, 16) are identical and balance second order free inertia forces.
