Abstract: Apparatus for converting between rotary motion and reciprocating linear motion includes a sleeve mounted for rotation about a predetermined axis, radially reciprocable pistons located radially outwardly of the sleeve, and axially reciprocable pistons located radially inwardly of the sleeve. The radial pistons are operatively connected to an outer diameter portion of the sleeve which is formed with a lobed cam surface having multiple angularly spaced lobes for simultaneous reciprocation of the radial pistons and rotation of the sleeve, and the axial pistons are operatively connected to a groove formed in the inside diameter portion of the sleeve for simultaneous reciprocation of the axial pistons and rotation of the sleeve.