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Photo of Southern Pacific MC-6 class cab forward mallet locomotive No. 4030.
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Photo of Southern Pacific MC-6 class cab forward mallet locomotive No. 4030.

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Southern Pacific Class MC-6 Mallet Consolidation Cab Forward Locomotive
Southern Pacific Company's MC-6 class of steam locomotives is made up of two batches: the first consisting of 15 locomotives weighing 435,800 lbs and built in 1912, the second consisting of 5 locomotives weighing 437,100 lbs and built in 1913. All of the locomotives were built by Baldwin Locomotive Works. This was the last class of 2-8-8-2 locomotives that Southern Pacific (SP) ordered as cab forward locomotives.

Locomotive number 4043, the newest of the early class of MC-6 locomotives, was displayed at the Panama-Pacific International Exposition along with SP's first locomotive, C. P. Huntington.

All but three of the locomotives in this class were rebuilt as the AC-3 class with modified (compound to simple) uniform cylinders of 22 in × 30 in (559 mm × 762 mm) by 1930. The last three were thus rebuilt in 1937. During the rebuild, 4¼-BL Worthington feedwater heaters were also installed on the fireman's side of the locomotives.

After their rebuilds, the locomotives were used through the end of World War II with the last one scrapped on August 20, 1949.

Southern Pacific Class MC-6 Overview
Type and origin
Power type: Steam
Builder: Baldwin Locomotive Works
Serial numbers: 38523–38534, 38711–38713, 39673, 39731, 39857, 39858, 39874
Build date s:October–December 1912 and April–May 1913
Total produced: 20

Configuration: 2-8-8-2 Mallet
UIC class: (1′D)D1′ h4v
Gauge: 4 ft 8 1⁄2 in (1,435 mm) standard gauge
Driver diameter 57 in (1,448 mm)
Axle load: 51,200 lb (23,223.9 kg; 23.2 t)
Adhesive weight: 400,700 lb (181,800 kg; 181.8 t)
Locomotive weight: 435,800 lb (197,700 kg; 197.7 t)
Total weight: 615,200 lb (279,100 kg; 279.1 t)
Fuel type: Fuel oil
Fuel capacity: 3,200 US gal (12,000 l; 2,700 imp gal)
Water capacity: 10,000 US gal (38,000 l; 8,300 imp gal)
 • Firegrate area: 60.4 sq ft (5.61 m2)
Boiler pressure: 200 psi (1.38 MPa)
Heating surface: 4,177 sq ft (388.1 m2)
​ • Heating area: 5,016 sq ft (466.0 m2)
Cylinders: Four
High-pressure cylinder: 26 in × 30 in (660 mm × 762 mm)
Low-pressure cylinder: 40 in × 30 in (1,016 mm × 762 mm)
Valve gear: Walschaerts
Performance figures
Tractive effort 94,880 lbf (422.05 kN)
Operator: Southern Pacific Company
Class: MC-6
Numbers: 4029 – 4048
First run: December 17, 1912
Retired: 1946 – 1949
Disposition: All rebuilt as AC-3 class; all of which were scrapped

See also:

Cab Forward Locomotives

Southern Pacific