A combination starter-generator device for a work vehicle includes an electric machine and a bi-directional gear set. The gear set is configured to receive rotational input from the electric machine and from the engine and to couple the electric machine and the engine in a first power flow direction and a second power flow direction. In the first power flow direction the gear set effects a first gear ratio, and in the second power flow direction the gear set effects a second gear ratio. In the first power flow direction, the gear set receives input power from the electric machine in a first clock direction and outputs power to the engine in a second clock direction opposite the first clock direction. In the second power flow direction, input power from the engine is in the second clock direction and output power to the electric machine is in the second clock direction.