| New Zealand DG and DH class | |
| Powertype: | Diesel-Electric |
| Builddate: | 1955 - 1956 |
| Builder: | English Electric and Vulcan Foundry / Robert Stephenson & Hawthorns, England |
| Locoweight: | 69LT |
| Weightondrivers: | DG DH |
| Uicclass: | A1A - A1A |
| Firstrundate: | 6 September 1955 |
| Lastrundate: | 16 May 1983 |
| Disposition: | 38 scrapped 4 preserved |
| Numinclass: | 31 DG 11 DH |
| Poweroutput: | 750hp gross, 685hp net |
| Tractiveeffort: | 260001NaN1 DG 290001NaN1 DH |
| Primemover: | English Electric 6SRKT Mark 2 |
| Enginetype: | four stroke, four valves per cylinder |
| Aspiration: | Turbocharged |
| Cylindercount: | I6 |
| Cylindersize: | 10x |
| Rpmrange: | 850 rpm |
| Tractionmotors: | Four EE 525/2A |
| Maxspeed: | 60mph |
| Locale: | All of New Zealand |
| Fleetnumbers: | 750 - 791 (original) 2007 - 2497 (TMS) |
| Length: | 45feet over headstocks |
| Width: | 8feet |
| Height: | 11feet |
| Fuelcap: | 400impgal |
| Wheeldiameter: | 3feet |
| Minimumcurve: | 2973NaN3 |
| Wheelbase: | 37feet total, 11feet bogie |
| Transmission: | electric |
| Multipleworking: | 110V, 10 notch electro-magnetic control |
| Locobrakes: | air |
| Trainbrakes: | air |
The New Zealand DG and DH class were classes of forty-two diesel-electric locomotives operated on New Zealand's rail network between 1955 and 1983.
Between 1978 and 1980, ten of these locomotives were rebuilt with new equipments in an attempt to modernise and extend their working lives. The locomotives continued to suffer from reliability issues brought about by electrical and mechanical failures.
The New Zealand Railways Department (NZR) initially ordered 31 DF class locomotives in the process of displacing steam motive power from main lines in New Zealand. However, this order was later amended to 10 DF and 42 DG class locomotives due to a shift in the NZR's dieselisation strategy.
The DG class locomotives were a smaller version of the DF class, with only one cab instead of two, and a similar Bulldog nose. Instead of assembling locomotives at its Preston works, English Electric allocated the final assembly to its sub-plants. This approach was also followed for many of that firm's diesel locomotives during the 1950s-60s. Works numbers 2254/E7821-2273/E7840 (NZR road numbers 750-769) were assembled at the Robert Stephenson & Hawthorns, while works numbers 2274/D353-2295/D374 (NZR road numbers 770-791) were assembled at the Vulcan Foundry, both being part of English Electric at the time.
The locomotives allocated in South Island were initially classified as DH as they were fitted with adjustable bogies that allowed a higher maximum axle weight and tractive effort.[1] By adjusting their spring beams, the DH locomotives were able to increase their adhesive weight to and the tractive effort to . Both DG and DH classes shared the axle loading of .
In August 1955, DG 750, along with an 88-seater railcar RM 100, a DF class locomotive, and a newly arrived Drewry DSB class shunting locomotive, was sent to the Wanganui Industrial Fair, marking the first regular outing of DG class locomotives. Following the completion of the Rimutaka Tunnel, the class took over workings in the Wairarapa area and on the Murupara Branch from the older DE class. As they were relatively low-powered, these locomotives usually worked in multiple, although they did occasionally run on their own.
As enough DA class locomotives were made available in the North Island, the DG locomotives based on that region were transferred progressively south with the introduction of the rail ferry GMV Aramoana in 1962. This relocation process was completed by 1976. In 1968, the DH class locomotives were converted to DG class standards and received the DG classification, allowing the DH classification to be re-used in 1978.
The class was usually relegated to "slave" status after the introduction of DJ class locomotives in 1968. The introduction of the new DF class in 1979 further displaced the class.
The introduction of the Traffic Monitoring System (TMS) in 1979 saw the locomotives being renumbered DG2007 - DG2497.
In the late 1970s, the DG class was reaching the end of its designated working life with a litany of problems:
In an attempt to modernise and extend the operational lifespan of the DG class locomotives for a decade to fifteen years,[3] Chief Mechanical Engineer Graham Alecock was instructed to create a proposal to equip them with new cabs that would be more crew-friendly and better equipped. The decision was made to rebuild DG 760 (later renumbered DG2111 with the implementation of the Traffic Monitoring System), which was due for an overhaul at the Hillside Workshops, as a prototype for the rebuilds. DG 760 was released from Hillside in August 1978 as the first of an eventual ten rebuilds to be completed between 1978 and 1980, when DG2330 was released into service in November 1980.
The NZR designed the new cab in-house and contracted its Westport Workshops to build them on behalf of Hillside, which led to some issues with fitting cabs to the locomotives. The cab was larger than the original DG cab, which required the front low nose to be shortened. The whole assembly had a pronounced box-like shape, with 45° angles to the cab roof and a low nose. The new cab had four windscreens instead of the original three, while the low nose had a larger doorway to access the new Westinghouse 26L air-brake equipment and also to give provision for a short walkway on either side of the nose. The small windows were the same as those used on the DX class locomotives to improve standardisation on locomotives.
In mechanical respects, the front traction motor blower was moved to a position above the main generator, and new thermostat valves were installed to prevent the overheating issues that had affected the locomotives under load. The original Westinghouse A7EL brake system was replaced by the more modern 26L system, which was actuated by a new push-button console in the cab. The traction motors were also upgraded, and welding repairs were carried out on the 6SKRT engine blocks. Some blocks were later sent to the United States for repairs using the Metalock treatment, which was later considered a failure as the blocks cracked again, rendering the treatment a waste of money.
The locomotives also underwent several minor changes. Steps were fitted to the rear 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 installed. The front ladders were also fitted to allow access to the cab windows, some of which were integrated into the sheet metal profile edge from the frame to the leading headstock. Both horns were relocated to the front of the cab, although the rebuilt DG 760 had three - two forward facing on the cab front, with one behind the cab.
Although the railway unions - the Locomotive Engineers Association (LEA) and the Engine-drivers, Firemen, and Cleaners Association (EFCA) - were pleased with the cab design, which took into account their input from the early design phases, the locomotives proved to be mechanically unreliable. They were put into service hauling freight trains on the Main South Line and occasionally on the Midland Line. Even though their new cab was designed with a provision to operate them over the Otago Central Railway in mind, very few of the re-cabbed locomotives ever worked on that line.
Ten additional DG class locomotives - nine built by Vulcan Foundry and one by RS&H - received an "A-grade" overhaul to work as trailing B-units for the rebuilt locomotives. These locomotives did not receive new cabs and, therefore, were not driven in regular service. Several other locomotives of this type also received the updated Westinghouse 26L brake system and the NZR-designed push-button control stand.
The locomotives continued to suffer from reliability issues caused by electrical and mechanical failures, and they were later prohibited from running with the Mitsubishi DJ class and General Motors DF class 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, DG 765, was treated on the fact it had an engine block in good condition.
By 1983, most of the unrebuilt DG class locomotives had been withdrawn from service, while the rebuilt ones continued until they either encountered mechanical issues or required major repairs. On August 28, 1983, the NZR ran a "Farewell to the DG Class" excursion between Christchurch and Arthur's Pass on the Midland line. The first and last DG class locomotives, rebuilt DG2007 and unrebuilt DG2468, hauled the excursion and marked the end of the original DG class in regular service. The following month, DG2007 failed when it threw a con rod through the engine block and was placed in storage, while DG2468 was sold to the Weka Pass Railway shortly after.
In 1983, Dunedin-based machinery dealers W. Rietveld Limited were contracted by the NZR to scrap the rebuilt DG class locomotives,[4] which were stored in Dunedin. At the time, these locomotives were mostly unserviceable due to mechanical failures or had been laid up with the arrival of more modern motive power. Some had their EE 525 traction motors removed by the NZR and sold to the National Federation of Railway Societies for other groups who owned the DG class locomotives.
The withdrawn locomotives were stored at the former sidings at Pelichet Bay and stripped of all useful parts before being 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 later followed by numbers 2007, 2290, 2111, and 2439. The last two, DG2128 and DG2330 remained at the Dunedin Locomotive Depot for a while 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 - they were the last two rebuilt DG class locomotives in existence.[5]
Rietveld did not scrap some of the unique cabs from these locomotives. Instead, they removed them intact and held several at their Abbotsford reclaim site, including that of DG2007. Darryl Bond, a part-owner of DG2376, purchased the cab of DG2140.
thumb|A NZ120 model DG class locomotive.With the phasing out of the DG class in the early 1980s, several locomotives were purchased for preservation:[6]
In addition: