The original engines were built in Belfast by Harland & Wolff under licence from Burmeister & Wain known as the "Harlandic" type.
In 1953 spare parts supply difficulties and engine age prompted the NSWGR to re-engine the fleet with four 6-110 GM diesel engines rated at at 1800 rpm coupled in pairs driving Allison torque converters to the inner axle of each bogie.