South African Class 91-000

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South African Class 91-000
Class 91-000 no. 91-003.jpg
Numbers 91-003 and 91-009 on the limestone train from Loerie PPC to New Brighton
Type and origin
Power type Diesel-electric
Designer General Electric
Builder General Electric
Serial number 38603-38622
Model GE UM6B
Build date 1973
Total produced 20
AAR wheel arr. B-B
UIC class Bo'Bo'
Imperial class Bo-Bo
Gauge 2 ft (610 mm) narrow
Wheel diameter 838 mm (33.0 in)
915 mm (36.0 in) Bigfoot
Wheelbase 7,290 mm (23 ft 11.0 in)
7,314 mm (24 ft 0 in) Bigfoot
 • Bogie 2,108 mm (6 ft 11.0 in)
2,082 mm (6 ft 10.0 in) Bigfoot
Pivot centres 5,232 mm (17 ft 2.0 in)
 • Over couplers 10,580 mm (34 ft 8.5 in)
Width 2,564 mm (8 ft 4.9 in)
Height 3,632 mm (11 ft 11.0 in)
Axle load 12,000 kg (26,000 lb)
Adhesive weight 48,000 kg (106,000 lb)
Loco weight 48,000 kg (106,000 lb) max
Fuel type Diesel
Fuel capacity 1,600 litres (350 imp gal)
Prime mover Caterpillar D-379
RPM range 650-1,365
 • RPM idle 650
 • Maximum RPM 1,365
Engine type 4-stroke diesel
Aspiration Schwitzer 4ME 455 turbocharger
Generator 6 pole GE 5GT-601C1
Traction motors Four GE 5GE-778AI DC 4 pole
Two GE 5GE-761-A13 DC 4 pole Bigfoot
 • Rating 1 hour 410A, 665A Bigfoot
 • Continuous 395A @ 14 km/h (8.7 mph)
655A @ 15 km/h (9.3 mph) Bigfoot
Cylinders V8
Gear ratio 13:68:1 double reduction
MU working 3 maximum
Loco brake 28-LV-1 with vigilance control
Train brakes Westinghouse 4CD2UC compressor/exhauster
Air reservoir cap 500 litres (110 imp gal)
Compressor cap 0.036 m3/s (1.3 cu ft/s)
Exhauster cap 0.072 m3/s (2.5 cu ft/s)
Couplers Willison
AAR knuckle (Bigfoot)
Performance figures
Maximum speed 50 km/h (31 mph)
Power output:
 • Starting 520 kW (700 hp)
 • Continuous 480 kW (640 hp)
Tractive effort:
 • Starting 108 kN (24,000 lbf) @ 25% adh.
 • Continuous 86 kN (19,000 lbf) @ 15 km/h (9.3 mph)
Factor of adh.:
 • Starting
 • Continuous 20%
Loco brakeforce 60% ratio @ 345 kPa (50.0 psi)
Dynamic brake peak effort 85 kN (19,000 lbf) @ 14 km/h (8.7 mph)
Operators South African Railways
Transnet Freight Rail
RRL Grindrod
Class Class 91-000
Number in class 20
Numbers 91-001 to 91-020
Delivered 1973
First run 1973

The South African Railways Class 91-000 of 1973 is a narrow gauge diesel-electric locomotive.

Between September and December 1973, the South African Railways placed twenty Class 91-000 General Electric type UM6B diesel-electric locomotives in service on its narrow gauge Avontuur Railway line, between Port Elizabeth in the Eastern Cape and Avontuur in the Western Cape. Some of them later also worked on the Alfred County Railway line, out of Port Shepstone in KwaZulu-Natal.[1][2]


The Class 91-000 GE type UM6B diesel-electric locomotive was designed and built for the South African Railways (SAR) by General Electric (GE) in Erie, Pennsylvania. Twenty locomotives were delivered between September and December 1973, numbered in the range from 91-001 to 91-020. It was designed for 2 ft (610 mm) narrow gauge and is the largest two foot gauge diesel-electric locomotive in the world, at an average weight of 44,000 kilograms (97,000 pounds).[3]

Works plate on no. 91-002

The usual practice was to have locomotive builder’s works plates attached to the locomotive’s frame below the cab windows. The Class 91-000 locomotives, however, had their works plates mounted on each side of the long hood. With the exception of numbers 91-001 (GE 38604), 91-002 (GE 38603), 91-016 (GE 38619) and 91-017 (GE 38618), the Class 91-000 works numbers are in sequence with their running numbers. It is very likely, however, that this was the result of body panels being swapped between locomotives during overhauls.[4]


As a result of the severe clearance problems presented by the two foot gauge, it was not possible to follow the usual practice of axle-hung traction motors. Special bogies had to be designed, with the traction motors mounted between the axles, with one traction motor on each side of each bogie.[2]

Willison coupler

The locomotives are both air and dynamically braked, while a lag control was incorporated into the train’s brake pipes to prevent bunching of the wagons upon braking and snatching upon restarting. This, combined with the cabling required for multi-unit control, resulted in altogether seven cable connections between consisted units.[2]

The Class 91-000 also introduced the new Willison or SA3 coupler, which eventually replaced the old Norwegian Hook type coupler on South African narrow gauge rolling stock.[2]

End of the steam era[edit]

The Class 91-000 replaced the ageing Class NG G13 and NG G16 Garratts and Class NG15 2-8-2 Kalahari steam locomotives, which had been working the Langkloof narrow gauge line until then. It is the only diesel-electric locomotive type to have operated on South Africa’s narrow gauge lines.[2]


South African Railways[edit]

These locomotives served nearly exclusively on the Langkloof line, but between 1992 and December 2003, a few of them also worked on the Alfred County Railway (ACR) narrow gauge line out of Port Shepstone. The locomotives which were transferred to and from Natal, usually travelled all the way from Port Elizabeth under their own power on what became known as Bigfoot bogies, which were actually 3 ft 6 in (1,067 mm) Cape gauge Class 36-000 GE type SG10B bogies. These Bigfoot bogies were also used under the Class 91-000 locomotives whenever they had to be exchanged for maintenance purposes, sometimes running under their own power, sometimes hauled dead.[4]

Over the years since the Class 91-000 was commissioned, the demand for rail services declined steadily on both the ACR and the Langkloof lines. Still, even though road transport had triumphed over rail transport in respect of fruit traffic from the Langkloof by the 1980s, the eastern part of the line remained busy for some years, hauling limestone from Loerie. When the quarry, which fed Loerie station by cableway, was closed, however, the fate of the narrow gauge line was virtually sealed.[5]

Despite this, in the narrow gauge line’s centenary year in 2003, Spoornet still stated its commitment to keep the line in service, by undertaking to invest in infrastructure and technology. As recently as September 2005, there was even talk of extending the 107 kilometres (66 miles) branchline from Loerie further up the Gamtoos valley, to assist farmers who had difficulty moving their produce.[6]

By 2009, however, Transnet Freight Rail (TFR) had decided that narrow-gauge railway operations were no longer in its "core line of business" and began to cull the herd, by putting some of the Class 91-000 locomotives up for auction. Of the twenty locomotives built, eighteen were still in operation by 2009, two having been withdrawn after accident damage.[4]

At least one Class 91-000 locomotive, no. 91-010, was still in service with TFR by 2013. It was mounted on Bigfoot bogies, of which only one was equipped with traction motors, and equipped with AAR knuckle couplers, for use as a shunting locomotive at the Swartkops electric locomotive depot in Port Elizabeth. The rest of the fleet which were still on the TFR roster, were standing idle, staged at the narrow gauge depot at Humewood Road in Port Elizabeth.

Industrial service[edit]

Five locomotives were sold to RRL Grindrod, a joint venture between Solethu Investments, a South African Black Economic Empowerment (BEE) rail logistics company, and Grindrod Limited, a shipping and logistics group, for use at Welkom in the Free State to haul mine hoppers. Four of them were renumbered in the range from RRL 91-01 to 91-04 and their original narrow gauge bogies were cut in half and widened to 3 ft 6 in (1,067 mm) Cape gauge.[7][8][9] The fifth was the accident-damaged no. 91-009, which was completely rebuilt as a 700hp Caterpillar engine-generator.

Three more locomotives were sold on auction on 11 July 2013. These were purchased by a Port Elizabeth scrap merchant for rebuilding and resale.

Tourist/Heritage Service[edit]

Two locomotives, numbers 91-006 and 91-007, were transferred to Patons Country Railway in 2015. They were in use on narrow gauge tourist trains from Allwoodburn Siding at Ixopo in KwaZulu-Natal in December 2015 and January 2016. 91-010 has been sold to Sandstone Estates in operating condition. It arrived at their facility on October 31st 2016.

Works numbers[edit]

The Class 91-000 builder's works numbers and their disposal are listed in the table.[4]


All the Class 91-000 locomotives were delivered in the SAR Gulf Red and whiskers livery. The main picture shows numbers 91-003 and 91-009 in that livery, on the limestone train from Loerie PPC to New Brighton on 8 April 1985. They were later all repainted in the Spoornet orange livery. Only one, no. 91-001, was again repainted in the Spoornet blue livery with outline numbers.


  1. ^ South African Railways Index and Diagrams Electric and Diesel Locomotives, 610mm and 1065mm Gauges, Ref LXD 14/1/100/20, 28 January 1975, as amended
  2. ^ a b c d e Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 144. ISBN 0869772112. 
  3. ^ Class 91-000 page from the SAR Index and Diagrams of Electric and Diesel Locomotives, Ref LXD 14/1/100/20, Issued 28/1/75
  4. ^ a b c d Middleton, John N. (2002). Railways of Southern Africa Locomotive Guide - 2002 (as amended by Combined Amendment List 4, January 2009) (2nd, Dec 2002 ed.). Herts, England: Beyer-Garratt Publications. pp. 38–39, 45. 
  5. ^ Railways Africa, 18 Jan 2007: Revamping the Apple Express
  6. ^ 100 Years of Being at the Heart of It All, Spoornet brochure, Circa 2003
  7. ^ Railways Africa, 8 Mar 2007: Langkloof narrow-gauge
  8. ^ Railways Africa, 19 Apr 2010: Class 91 Diesels in the OFS
  9. ^ Railways Africa, 5 Feb 2010: Transnet Freight Rail Auction Results