Electric machine assemblies and methods of manufacturing and operating electric machine assemblies for internal combustion engines are provided. The electric machine assembly includes an electric machine configured to generate electric current by induction via a prime mover causing rotation of one of a rotor and a stator with respect to the other one of the rotor and the stator. The electric machine assembly also includes a torque transmitter including a rotating output driver coupled to the prime mover of the electric machine. The torque transmitter includes a rotating input driver configured to receive a rotary input transmitted from a crankshaft of an internal combustion engine. The rotating input driver is coupled to the rotating output driver to actuate the rotating output driver at a plurality of gear ratios.