Abstract: A rotor comprises two rotor sections mounted coaxially on a shaft for limited axial movement relative to each other. The two sections are slightly spaced axially from each other and one defines a peripheral porting surface engaging a second porting surface defined by a porting member. The rotor has a plurality of bores each carrying a piston and including a first portion defined by one of the rotor sections, a second portion defined by the other of the rotor sections, and an intermediate portion extending between the rotor sections. The pistons engage a cam comprising a sheet pressed into a configuration including a plurality of coaxial annular sheet portions. One sheet portion defines the undulating cam surface; two other sheet portions extend parallel to each other and perpendicular to the one portion from the opposite sides of the one portion.