Abstract: A piston-cylinder device, such as a Rankine cycle engine, is provided with one or more variable displacement cylinders and variable stroke pistons for accommodating loads of variable torque. Cylinder displacement is varied by a movable cylinder head internally of the cylinder and auxiliary to a fixed cylinder head, and piston stroke is varied by a variably fulcrumed lever linking piston connecting rods with a crankshaft. For the engine particularly, load torques are continually sensed and cylinder displacement adjusted accordingly. In turn, the position of the movable cylinder head is continually sensed, and the lever fulcrum adjusted accordingly.