El Paso & Southwestern / Southern Pacific 4-8-2 "Mountain" Locomotives in 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".


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 Rail Data Exchange. 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)

Data from 1930 Locomotive Cyclopedia of American Practice, p. 115. See also "Southern Pacific Heavy 4-8-2 Type Locomotive", Railway and Locomotive Engineering, Volume XXXVII [37], No 3 (March 1924), pp. 69-71; and "4-8-2 Locomotive for Long Passenger Runs," Railway Review, Volume 74, (9 February 1924), pp. 250-256 . (Thanks to Chris Hohl for his 6 May 2020 email providing the R&LE link, original tender w-eights and capacities, and correct driver diameter). Works numbers were 64891-64900 in October 1923, 65380-65397 in March 1924.

First batch built by Alco-Schenectady (works numbers were 64891-64900 in October 1923; 65380-65397 in March 1924. Later batches in SP shops up through 1929. Each year's batch received a different class ID. 4328-4345 were Mt-3, 4346-4366 were Mt-4, and 4367-4371 were Mt-5.

Another six (Mt-2; see Locobase 1403) were built by and for the El Paso & Southwestern with different running gear;

The Espee Mountains were considered to have been a very successful class. The design's first locomotives went into service over the 815 mile (1,312 km) main line between Los Angeles and El Paso (Tex) without changing locomotives. They were expected to average 12,000 miles (19,320 km) a month.

The usual requirements for large express passenger locomotives in the US were specified by general superintendent of motive power George McCormick and assistant mechanical engineer Frank Russell. "Ample boiler capacity for the long-sustained runs" and maximum tractive power within weight limits. Special high-tensile cast-steel components allowed these characteristics while minimizing weight as much as possible. Even the cab was narrowed by eliminating the doors in the front of each side and providing windows. (Engine crew now used handholds "conveniently located" in the eaves as they sidled along the edges of the cab floor.)

All were delivered with Worthington 4-B feed water heaters mounted on the left side of the boiler; 4 1/4 BLs were fitted to 4359-4371 . A type C-1 trailing truck booster contributed 10,100 lb to low-speed tractive effort. The booster took its steam from the steam chest rather than the dome, thus substituting more powerful superheated steam for the saturated steam available in the dome.

To reduce track stress, the engines employed a constant-resistance centering device along with Franklin lateral motion devices in the front drivers. As a result, side forces dropped on tangent (straight) track while curves induced less stress. Another feature was the low ratio of weight--1 in 201 lb (91.2 kg)--of the reciprocating parts to the total locomotive weight, significantly better than "the ratio of 1 to 160, which is considered good practice."

They were oil-fired engines that trailed several different kinds of Vanderbilt tenders, including some holding 16,152 US gallons (61,135 litres) water, 4,692 gallons (17,759 litres) oil.

Some were later fitted with skyline casings around the boiler and resembled the better-known GS series of express passenger 4-8-4s.

Of Schenectady's brood, all survived to be scarpped in 1954-1959 except 4317, which was wrecked in October 1952.

Principal Dimensions by Steve Llanso of Sweat House Media

Locobase ID1403 228
RailroadEl Paso & Southwestern (SP)Southern Pacific (SP)
Number in Class671
Road Numbers410-415/4385-43904300-4371
Number Built671
Valve GearBakerWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)19.50 / 5.9420 / 6.10
Engine Wheelbase (ft / m)43.58 / 13.2842.25 / 12.88
Ratio of driving wheelbase to overall engine wheelbase 0.45 0.47
Overall Wheelbase (engine & tender) (ft / m)83.37 / 25.4183.50 / 25.45
Axle Loading (Maximum Weight per Axle) (lbs / kg)61,800 / 28,032
Weight on Drivers (lbs / kg)262,000 / 118,841246,000 / 111,584
Engine Weight (lbs / kg)391,000 / 177,355368,000 / 166,922
Tender Loaded Weight (lbs / kg)257,500 / 116,800242,400 / 109,951
Total Engine and Tender Weight (lbs / kg)648,500 / 294,155610,400 / 276,873
Tender Water Capacity (gals / ML)12,300 / 46.5912,000 / 45.45
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)20 / 183790 / 14,345
Minimum weight of rail (calculated) (lb/yd / kg/m)109 / 54.50103 / 51.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)73.50 / 186773 / 1854
Boiler Pressure (psi / kPa)210 / 14.50210 / 14.50
High Pressure Cylinders (dia x stroke) (in / mm)29" x 30" / 737x76228" x 30" / 711x762
Tractive Effort (lbs / kg)61,273 / 27793.0057,511 / 26086.58
Booster (lbs)10,100
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.28 4.28
Heating Ability
Tubes (number - dia) (in / mm)234 - 2.25" / 57223 - 2.25" / 57
Flues (number - dia) (in / mm)50 - 5.5" / 14045 - 5.5" / 140
Flue/Tube length (ft / m)22 / 6.7121.50 / 6.55
Firebox Area (sq ft / m2)461 / 42.84355 / 32.98
Grate Area (sq ft / m2)84.20 / 7.8375.70 / 7.04
Evaporative Heating Surface (sq ft / m2)5060 / 470.264556 / 423.42
Superheating Surface (sq ft / m2)1380 / 128.251162 / 107.99
Combined Heating Surface (sq ft / m2)6440 / 598.515718 / 531.41
Evaporative Heating Surface/Cylinder Volume220.67213.10
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 L122,19720,064
Power MT747.11719.24

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