Abstract: A heat engine system with a rotating wheel assembly. The wheel assembly rotates through an expansion zone and a contraction zone. The expansion zone heated. The contraction zone is not heated and may be actively cooled. Weights are supported by the wheel assembly. Each of the weights are movable from a first position that is a first distance from the wheel's center to a second position that is a farther second distance from that center. A temperature activated piston is coupled to each of the weights. Each of the temperature activated pistons move one of the plurality of weights between its first position and its second position as each temperature activated piston rotates on the wheel assembly through the expansion zone and the contraction zone. The movement of the weights dynamically alters the center of mass for the wheel assembly and causes it to turn.