An engine includes a first power source configured to drive a first power input, a power output, and a transmission engaged with the first power input and the power output. The transmission includes an epicyclic gear train engaged with the first power input and selectively engageable with the power output. A brake is engageable in a drive condition with the epicyclic gear train to transfer power from the first power input to the power output. The brake in a start condition is disengageable to decouple the first power input from the power output. A start assist motor associated with a second power source is engaged with the transmission to rotate the power output.