Abstract: A rotary crankless machine in which there is a rotary shaft, a rotary cylinder block, and a stationary housing, all concentrically disposed about a common axis and in which the housing has a central annular manifold block with inlet and outlet passages disposed midway between the ends of the housing. The rotary cylindrical block and shaft are rotatably coupled together and the rotary cylindrical block has a pair of sets of inwardly directed cylinders each of which extends from adjacent the outer wall of the cylinder block inwardly towards the manifold block and disposed so as to be selectively in communication with the inlet and outlet passages of the manifold block as the cylinder block rotates, and in each of which a piston is reciprocated. The longitudinal axis of each cylinder is substantially inclined inwardly with respect to the common axis of the machine and with respect to the transverse plane perpendicular to the axis.