An engine assembly includes a crankshaft having a first axis of rotation and a crankpin offset from the first axis of rotation. A second shaft is offset from the crankshaft and has a second axis of rotation. A piston is movable in a cylinder between a top dead center position and a bottom dead center position to drive the crankshaft. A connecting rod extends from the piston. A four-jointed linkage assembly pivotably connects the connecting rod, crankshaft, and second shaft. A drive system operatively connects the crankshaft and the second shaft to drive the second shaft via the crankshaft. A phasing mechanism connects the drive system and the second shaft and is controllable to vary the rotational position of the second shaft relative to the crankshaft.