A crankcase for a locomotive air compressor including a body defining an interior space, a port in fluid communication with the interior space of the body, a valve receiving portion adjacent to and surrounding the port, and an oil drain valve engaged with the valve receiving portion and having a flow passageway in fluid communication with the port. The oil drain valve has an open position and a closed position, such that the oil drain valve in the open position allows oil to flow from the interior space of the body through the flow passageway, and the oil drain valve in the closed position prevents the flow of oil from the interior space of the body through the flow passageway. A method for installing a locomotive air compressor having the crankcase and oil drain valve is also disclosed.