Abstract: A rotary pump or motor is disclosed which includes a housing which defines a substantially cylindrical cavity having a central axis. A pair of stators are secured at each end of the cylindrical cavity and each stator has a cam surface defined by at least a pair of surface peaks circumferentially alternating with at least a pair of surface valleys, the stator cam surfaces being spaced apart and opposed to one another. A substantially cylindrical rotor having length and diameter dimensions is disposed for rotation within the cavity between the stators. The rotor includes first and second end cam surfaces configured for mating engagement with adjacent stator cam surfaces. Each rotor end face is a cam surface defined by at least a pair of surface peaks circumferentially alternating with at least a pair of surface valleys. A shaft is connected to the rotor for rotation therewith within the cavity while permitting axial movement between the shaft and the rotor.