The 620 & 720 class railcars are a Diesel Multiple Unit train used in the latter stages of their life by CityRail, primarily on its Hunter Valley line. They were also used on the Toronto Railway Line before its closure. The trains have since been phased out in favour of the newer Hunter railcar model. The 620/720 railcars were built by New South Wales Government Railways (NSWGR) from 1961 to 1968. There were many variations of this railcar, but coded differently.
Five of the eighteen power cars were originally fitted with two 250 horsepower Rolls-Royce C Series horizontal in-line eight cylinder, four stroke diesel engines coupled to automatic lock-up torque converters. The next twelve had two 250 horsepower General Motors Detroit Diesel 110 Series in-line six cylinder, two stroke diesel engines coupled to similar transmissions. The last unit 638/738 was intended for use on the Grafton-Murwillumbah section hauling an EPT trailer. This unit was fitted with two 280 horsepower Cummins in-line six cylinder, four stroke diesel engines coupled to automatic lock-up torque converters. Scottish-made Cummins engines with Voith lock-up torque converter transmissions were retrofitted to all units in the 1980s. Straight air brakes with a special emergency feature and miniature automatic couplings were fitted as standard equipment. The Department of Railways' Water Supply Workshops at Chullora gained experience in lightweight bodywork whilst building aircraft during World War 2. Consequently, these and all other in-house DMUs featured bodywork of largely aluminium composition. Whilst such bodywork is light and relatively strong, the NSW DMUs are considerably less crashworthy than contemporary steel and stainless steel coaches. However, this less-than-crashworthy characteristic is typical of early railcars, including those built by British Railways during the same period.
These railcars are similar to the Endeavour railcars as in layout, with one railcar having toilets (non-wheelchair accessible) and one with luggage space, with 2x2 seating instead of 3x2 seating found on Endeavours and the new Hunter Railcars. 620/720 railcars are non-airconditioned, however, windows can be opened for ventilation. Gas heaters and fans can be operated within the car. The cars retain an interior similar to the 1960s setup with which they were delivered, with older seats still having the NSWGR markings. In the later period before they were withdrawn, elements were introduced to prevent windows being opened widely (and body parts protruded) and the exit doors from being opened mid journey. Prior to this, doors were frequently opened for ventilation.
All sets were withdrawn in 2007, with the last service running on October 29 from Newcastle to Paterson and return. Only a hand few were preserved. Set 621/721 was subsequently allocated to The Rail Motor Society at Paterson which have been restored to operational condition in the Indian red colour scheme, whilst set 623/723 was allocated to the NSWRTM as a static display. Others are in various collections in a non-operative state. 631/731 is now RailCorp's Mechanised Track Patrol Vehicle, numbered ML070