A combination starter-generator device is provided for a work vehicle having an engine. The starter-generator device includes an electric machine; and a gear set 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. The gear set is configured to operate in one of multiple relatively high-torque, low-speed start gear ratios in the first power flow direction and a relatively low-torque, high-speed gear ratio in the second power flow direction.