A hydraulic engine system includes a first hydraulic pump-motor coupled to an engine and a second hydraulic pump-motor coupled to an electric machine. A hydraulic link fluidly connects the first and the second hydraulic pump-motors. During a cranking operation mode, the electric machine operates as a motor and transfers power via the second hydraulic pump-motor, the hydraulic link and the first hydraulic pump-motor to provide cranking torque to the engine. During a generator operation mode, the power generated by the engine is transferred via the first hydraulic pump-motor, the hydraulic link, and the second hydraulic pump-motor to the electric machine, operating as a generator, to generate electricity.