A variable-stroke reciprocating internal combustion engine, the engine having an engine shaft and a piston configured to reciprocate within a cylinder chamber having an axis, each piston having a first piston part operable to move in unison with or separately from a second piston part to define piston strokes for different thermal functions of the engine, includes an 0 assembly pivotally coupled to the first piston part at a copy point and an actuator coupled to the assembly, wherein the actuator is operable to control motion of the assembly to thereby define substantially linear movement of the copy point along the cylinder chamber axis.
