El Paso & Southwestern / Southern Pacific 4-8-2 "Mountain" Locomotives of the USA

The first 28 "Mountains" on the Southern Pacific Lines were built by the American Locomotive Company and were delivered during 1923 and 1924. These locomotives were designated Class Mt-1 and assigned road numbers 4300 through 4327. They had 28 x 30 cylinders, 73" drivers, a 210 psi boiler pressure, a tractive effort of 57,510 lbs and weighed 368,000 pounds. Later, in 1924 another six "Mountains" were delivered from ALCO. These six (road numbers 4385 through 4390) were designated Class Mt-2 and were similar to the Class Mt-1s, but had a 225 psi boiler pressure and a tractive effort of 61,620 pounds.

The Sacramento General Shops of the Southern Pacific built 49 "Mountains" between 1925 and 1930. These were built in three batches: road numbers 4385 through 4345 designated Class Mt-3 in 1925 and 1926, road numbers 4346 through 4366 designated class Mt-4 built between 1926 and 1929 and road numbers 4367 through 4376 designated Class Mt-5 in 1929 and 1930. These locomotives were essentially copies of the Class Mt-1s. There are no surviving examples of the Southern Pacific "Mountains".

Roster by Richard Duley

ClassRoad NumbersYear BuiltBuilder

Class Details by Steve Llanso of Sweat House Media

Class L1s-62/Mt-2 (Locobase 1403)

Data from EP&SW 10- 1924 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Alco works number were 65788-65793 in September 1924.

Lone batch among Espee Mountains built for the El Paso & Southwestern (but delivered to the SP) with different running gear.

They were later rebuilt with 28" cylinders and Walschaert valve gear (as in the other batches). Firebox heating surface eventually included 22 sq ft (2.05 sq m) of arch tubes and 94 sq ft (8.75 sq m) in Nicholson thermic syphons. Steam admission came through 14" (356 mm) piston valves.

Class Mt-1/Mt-3/Mt-4/Mt-5 (Locobase 228)

First batch built by Alco-Schenectady in 1923; later batches in SP shops up through 1929. 69 built altogether, with another 6 (Mt-2; see Locobase 1403) built for the El Paso & Southwestern with different running gear; The Espee Mountains were considered to have been a very successful class. Oil-fired engine. Larger tender held 16,152 gal water, 4,692 gal oil.

Specifications by Steve Llanso of Sweat House Media
Locobase ID1403 228
RailroadEl Paso & Southwestern (SP)Southern Pacific (SP)
Number in Class669
Road Numbers410-415/4385-43904300-4327+
Number Built669
Valve GearBakerWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft)19.5020
Engine Wheelbase (ft)43.5842.25
Ratio of driving wheelbase to overall engine wheebase 0.45 0.47
Overall Wheelbase (engine & tender) (ft)83.3783.50
Axle Loading (Maximum Weight per Axle) (lbs)61,800
Weight on Drivers (lbs)262,000246,000
Engine Weight (lbs)391,000368,000
Tender Loaded Weight (lbs)257,500
Total Engine and Tender Weight (lbs)648,500
Tender Water Capacity (gals)12,30012,000
Tender Fuel Capacity (oil/coal) (gals/tons)204000
Minimum weight of rail (calculated) (lb/yd)109103
Geometry Relating to Tractive Effort
Driver Diameter (in)73.5073.50
Boiler Pressure (psi)210210
High Pressure Cylinders (dia x stroke) (in)29" x 30"28" x 30"
Tractive Effort (lbs)61,27357,120
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.28 4.31
Heating Ability
Firebox Area (sq ft)461355
Grate Area (sq ft)84.2075.70
Evaporative Heating Surface (sq ft)50604561
Superheating Surface (sq ft)13801162
Combined Heating Surface (sq ft)64405723
Evaporative Heating Surface/Cylinder Volume220.63213.33
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation17,68215,897
Same as above plus superheater percentage21,39519,076
Same as above but substitute firebox area for grate area117,14089,460
Power L122,19220,207
Power MT746.95724.37



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