New Zealand DG and DH class locomotive

Introduction

Due a change in government dieselisation strategy 21 of the original order for D^F class were changed to 42 D^G class locomotives, being a half-sized version of the D^F with only one cab instead of two, and a similar Bulldog nose. The English Electric Co, as they did with many of their diesel locomotives of the 1950s-60s, did not assemble them at the Preston works, but allocated the final assembly of build numbers 2254/E7821-2273/E7840 (road no. 750-769) to Robert Stephenson & Hawthorn and build numbers 2274/D353-2295/D374 (road no. 770-791) to Vulcan Foundry, both English Electric plants. The South Island allocated locomotives were initially classified D^H because they were fitted with adjustable bogies that allowed a higher maximum axle weight and tractive effort.

The first regular outing by a D^G class locomotive was that of D^G 750 in August 1955 when it was sent with 'Twin-set' railcar RM 100, a EE D^F class locomotive, and a newly arrived Drewry D^SB class shunting locomotive to the Wanganui Industrial Fair. Shortly after the class took over workings in the Wairarapa area following the completion of the Rimutaka Tunnel and also the Murupara Branch from the older D^E class. These locomotives usually worked in multiple as they were relatively low-powered, although they did occasionally run on their own.

With the arrival of enough D^A class locomotives in the North Island, the D^G locomotives from the North Island were transferred progressively south with the introduction of the rail ferry GMV Aramoana in 1962. As a result, the D^H class locomotives were converted to D^G class standards in 1968 and received the D^G classification, allowing the D^H classification to be re-used in 1978.

With the introduction of the D^J class in 1968 the class was usually relegated to "slave" status. The introduction of the new D^F class further displaced the class.

Rebuilds

In the late 1970s, the D^G class was reaching the end of its designated working life with a litany of problems:

In an attempt to modernise the D^G class and extend the working lives of the locomotives, Chief Mechanical Engineer Graham Alecock was requested to prepare a plan to equip the D^G class locomotives with new cabs that would be more crew-friendly and improved equipment. The decision was taken to rebuild D^G 760, then due for an overhaul at Hillside Workshops as the prototype for the rebuilds, which would be dubbed the 're-cabs' by enthusiasts.

The new cab was designed 'in-house' by NZR, who then contracted NZR's Westport Workshops to build them on Hillside's behalf. The cab itself was larger than the original D^G cab, which required the low nose at the front to be shortened. The whole assembly had a pronounced box-like shape, with 45° angles to the cab roof and low nose. The new cab featured four windscreens to the original three, while the low nose had a larger doorway to access the new Westinghouse 26L air-brake equipment and also gave provision for a short walkway on either side of the nose.

Mechanically, the locomotive's front traction motor blower was shifted to a position above the main generator, while new thermostat valves were fitted in an attempt to prevent the overheating problems that had plagued the locomotives under load. The original Westinghouse A7EL brake system was replaced by the more modern 26L system, actuated by a new push-button console in the cab. The traction motors were also upgraded, while welding repairs were conducted on the 6SKRT engine blocks. Several blocks were later sent to America for repairs using the Metalock treatment; this was later deemed to be a failure as the blocks again cracked and the Metalock treatment was seen as a waste of money.

The rebuilt locomotives also underwent several minor changes. Steps were fitted to the rear of the locomotives to allow access to the roof, external door handles and step-ladders were fitted to the middle set of engine-room doors, and an automated handbrake system was fitted. The locomotives also had front ladders fitted to allow access to the cab windows, some of which were integrated into the sheet metal profile edge from the locomotive frame to the leading headstock. Both horns were relocated to the front of the cab, although the rebuilt D^G 760 had three - two forward facing on the cab front, with one behind the cab.

D^G 760 was released from Hillside in August 1978 and was placed into service as the first of an eventual ten rebuilds to be completed between 1978 and the end of the program in 1980. While the LEA and EFCA were pleased with the cab design which took into consideration their input from the early design phases, the locomotive was perhaps not as mechanically successful as it should have been. Traction motor and engine problems still occurred, as well as occasional electrical faults. However, the locomotives were put into service hauling freight trains on the Main South Line and occasionally the Midland Line. Although the new cabs were designed with the Otago Central Railway in mind, very few of the re-cabbed locomotives ever worked this line.

Ten further D^G class engines - nine built by Vulcan Foundry and one by RS&H - were given 'A'-grade overhauls to work as trailing B-units for the rebuilt locomotives. These locomotives did not receive new cabs, and as such were not to be driven in regular service although photographs from this time show these locomotives were sometimes driven in regular service rather than turn a re-cabbed locomotive around. A number of other locomotives of this type also received the updated Westinghouse 26L brake system and NZR designed push-button control stand.

The class continued to suffer from reliability issues brought about by electrical and mechanical failures, and were later prohibited from running in multiple with the Mitsubishi DJ and General Motors DF locomotives, although they did sometimes run with the DJ class past this time. It was decided to start withdrawing those locomotives that had not been overhauled to provide parts for those that had, and so the first to be withdrawn, D^G 765, was withdrawn on the fact it had a good engine block.

By 1983, most of the original-cabbed DG class had been withdrawn, while the re-cabbed locomotives continued in service until they either suffered a mechanical failure, required major repairs or were withdrawn serviceable and placed in storage. On 28 August 1983, NZR operated a 'Farewell to the DG Class' excursion between Christchurch and Arthur's Pass on the Midland line. Hauled by recabbed DG 2007 and 'slave' unit DG 2468, the first and last DG class locomotives respectively, the excursion marked the end of the original DG class in regular service. The following month, DG 2007 failed when it threw a con rod through the engine block and was placed in storage, while DG 2468 was sold to the fledgling Weka Pass Railway shortly after.

Preservation

With the phasing out of the DG class in the early 1980s, several locomotives were purchased for preservation:

In addition:

Rietvelds DGs

The Dunedin machinery dealers W. Rietveld were contracted by New Zealand Railways in 1983 to scrap the re-cabbed DG class locomotives, which were then stored at Dunedin. These locomotives were largely unserviceable due to mechanical failures or had been laid up with the arrival of more modern motive power. Several of these locomotives had been lifted by NZR in order to gain access to their EE 525 traction motors, which had been sold to the National Federation of Railway Societies for distribution to other groups who owned DG class locomotives.

Rietveld used the former sidings at Pelichet Bay to house the withdrawn locomotives while they were stripped of all useful parts. The hulks would then be forwarded to Sims-PMI for scrapping at their Dunedin premises. The first four locomotives to be moved to Pelichet Bay were numbers 2036, 2140, 2105, and 2347. They were followed several months later by numbers 2007, 2290, 2111 and 2439. The last two, DG 2128 and DG 2330, remained at Dunedin Locomotive Depot for a time after that as Rietveld hoped to sell them to an overseas concern. This did not eventuate, and the two locomotives were towed to Pelichet Bay for stripping - the last two re-cabbed DG class to exist.

Several of the unique cabs from these locomotives were not scrapped but instead removed intact by Rietvelds, who in 2001 held several at their Abbotsford reclaim site, including that of DG 2007. The cab of DG 2140 was purchased by Darryl Bond, part-owner of DG 2376.