Abstract: A rotary piston machine with a chamber having a crank coaxial to a shaft, a rotary piston and a crown wheel for driving the piston. The crown wheel is coupled to the crank by a trunnion mounted in a bore of the crank. A fork joint is integral with the crown wheel. The bore axis is offset in the direction of rotation of the shaft with respect to the point of contact of the piston on the wall of the chamber. A spring bears on a shoe integral with the crown wheel and on the crank so that the line of force of the spring passes through the axis of the shaft and is prependicular to the straight line connecting the center of the piston and the center of the trunnion.