Abstract: A hydraulic machine which can exchange hydraulic fluid pressure with rotational motion of an input/output means, having a radial arrangement of a plurality of hydraulic piston and cylinder assemblies about a crankshaft, the hydraulic cylinder and piston assemblies being longitudinally spaced along the crankshaft; and a means for varying eccentricity of the crankshaft whereby reciprocal motion of the pistons within the respective hydraulic cylinders is consequential to rotational motion of the crankshaft about the longitudinal axis of the crankshaft.