South African Class MJ1 2-6-6-0

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South African Class MJ1 2-6-6-0
SAR Class MJ1 1673 (2-6-6-0).jpg
SAR Class MJ1 no. 1673, circa 1930
Type and origin
Power type Steam
Designer South African Railways
Montreal Locomotive Works
Builder Montreal Locomotive Works
Serial number 58427-58434
Model SAR Class MJ1
Build date 1918
Total produced 8
Configuration 2-6-6-0 Mallet
Gauge 3 ft 6 in (1,067 mm) Cape gauge
Leading dia 28.5 in (724 mm)
Driver diameter 42.75 in (1,086 mm)
Wheelbase Total: 60 ft 8.25 in (18,498 mm)
8 ft 4 in (2,540 mm) per coupled set
32 ft 8 in (9,957 mm) total
4 ft 7 in (1,397 mm) bogie
17 ft 11 in (5,461 mm) total
Length 68 ft 7.125 in (20,907 mm)
Height 12 ft 6.125 in (3,813 mm)
Axle load 14.1 long tons (14.3 t) on 3rd driver
Adhesive weight 81 long tons (82.3 t)
Loco weight 88.5 long tons (89.9 t) w/o
Tender weight 50.9 long tons (51.7 t) w/o
49,116 lb (22.3 t) empty
Loco & tender weight 139.4 long tons (141.6 t) w/o
172,400 lb (78.2 t) empty
Tender type LP
* 2 axle bogies
* 34 in (864 mm) wheels
* Length 27 ft 0.25 in (8,236 mm)
Fuel type Coal
Fuel capacity 10 long tons (10.2 t)
Water cap 4,250 imp gal (19,300 l)
 • Firegrate area
40 sq ft (3.716 m2)
Boiler As built:
5 ft 2.25 in (1,581 mm) inside diameter
17 ft 0.375 in (5,191 mm) inside length
7 ft 9.125 in (2,365 mm) pitch
5 ft 1.5 in (1,562 mm) inside diameter
17 ft 0.25 in (5,188 mm) inside length
7 ft 9.125 in (2,365 mm) pitch
Boiler pressure 200 psi (1,380 kPa)
Heating surface 2,042 sq ft (189.708 m2) as built
1,913 sq ft (177.724 m2) reboilered
 • Tubes As built:
146 tubes 2 in (51 mm) diameter
22 tubes 5.375 in (137 mm) diameter
1,906 sq ft (177.073 m2)
151 tubes 2 in (51 mm) diameter
18 tubes 5.5 in (140 mm) diameter
1,780 sq ft (165.367 m2)
 • Firebox 136 sq ft (12.635 m2) as built
133 sq ft (12.356 m2) reboilered
 • Heating area
413 sq ft (38.369 m2) as built
350 sq ft (32.516 m2) reboilered
Cylinders Four
High-pressure cylinder 16.5 in (419 mm) bore
24 in (610 mm) stroke
Low-pressure cylinder 26 in (660 mm) bore
24 in (610 mm) stroke
Valve gear Walschaerts
Performance figures
Tractive effort 37,950 lbf (169 kN) at 50% pressure
Operators South African Railways
Class Class MJ1
Number in class 8
Numbers 1666-1673
Delivered 1918
First run 1918
Withdrawn 1960

The South African Railways Class MJ1 2-6-6-0 of 1918 is a steam locomotive.

In 1918 the South African Railways placed eight Class MJ1 Mallet articulated compound steam locomotives with a 2-6-6-0 wheel arrangement in branchline service.[1][2][3]


Because of the difficulties experienced by the usual British and German suppliers to build new locomotives during World War I, orders for the Class MJ1 2-6-6-0 Mallet articulated compound steam locomotive were placed with Montreal Locomotive Works (MLW) in Canada. The locomotive was designed by MLW, based on the specifications for the Class MJ Mallet that was designed by D.A. Hendrie, the Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 to 1922. Eight of these branchline locomotives were built and delivered by MLW in November 1918, numbered in the range from 1666 to 1673.[1][3]

They were superheated, had Walschaerts valve gear and, like the Class MJ Mallets, had Belpaire fireboxes but slightly larger boilers. When compared to the Class MJ, a distinguishing feature of the Class MJ1 was the sandbox mounted on the boiler in North American style. In general appearance they were similar to the Class 14C and Class 15B 4-8-2 locomotives that were also built by MLW in 1918.[1][3]

The Class MJ1 was the last Mallet locomotive class to be placed in service by the SAR and all its subsequent new articulated locomotives were to be Modified Fairlies and Garratts.[4]

Compound expansion[edit]

In a compound locomotive steam is expanded in phases. After being expanded in a high pressure cylinder and having then lost pressure and given up part of its heat, the steam is exhausted into a larger volume low pressure cylinder for secondary expansion, after which it is exhausted through the smokebox. By comparison, in the more usual arrangement of simple expansion, steam is expanded just once in any one cylinder before being exhausted through the smokebox.[1][5]

In the compound Mallet locomotive, the rear set of coupled wheels are driven by the smaller high pressure cylinders which are fed steam from the steam dome. Their spent steam is then fed to the larger low pressure cylinders that drive the front set of coupled wheels.[1][3]


The Class MJ1 was also intended for branchline working and joined the Class MJ Mallets in service in the Eastern Cape. All eight were still in service by March 1948, but they were all withdrawn from service by 1960.[1][3][4]


  1. ^ a b c d e f Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 36–37. ISBN 978-0-7153-5427-8. 
  2. ^ South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
  3. ^ a b c d e Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 88. ISBN 0869772112. 
  4. ^ a b Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 24–25. ISBN 0715386387. 
  5. ^ Compounding Steam Engines