St Louis-San Francisco 4-8-2 "Mountain" Locomotives of the USA

The St. Louis - San Francisco Railway bought a total of thirty 4-8-2s from the Baldwin Locomotive Works to be used in passenger service. Fifteen (road numbers 1500 through 1514) were delivered in 1923, five (road numbers 1515 through 1519) came in 1925 and the final ten (road numbers 1520 through 1529) arrived in 1926.

All thirty of these "Mountains" had 28 x 28 cylinders, 69" drivers, a 210 psi boiler pressure, a tractive effort of 56,800 lbs and total locomotive weight as shown in the chart below.

During the late 1930s, the SLSF needed new locomotives, and money was tight, so the West Springfield Shops undertook a project to build a total of 34 4-8-2s from older locomotives. The first eleven of these rebuilds, outshopped in 1936 and 1937, were built from used 2-10-2 parts and were assigned road numbers 4300 through 4310. They had 27 x 30 cylinder, 70" drivers, a boiler pressure of 250 psi, a tractive effort of 66,400 lbs and weighed 431,110 pounds.

Another 23 4-8-2s were built using the boilers from 2-10-2s between 1939 and 1942. These locomotives were assigned road numbers 4400 through 4422 and had 29 x 32 cylinders, 70" drivers, a boiler pressure of 210 psi, a tractive effort of 68,600 lbs and weighed a whopping 449,760 pounds. They were the heaviest Mountains ever built. Locomotives numbers 4400 through 4412 were built as oil burners and numbers 4413 through 4422 burned coal.

There are six surviving SLSF "Mountains".

Number 1522 was donated to the Museum of Transportation in the early 1950s. It was restored to operating condition by a volunteer group known as the St. Louis Steam Train Association and has run several excursions. Today, it is undergoing a major overhaul and is scheduled to run again in May of 1999.

Roster by Richard Duley

Road NumbersYear BuiltBuilderLocomotive Weight
1500 - 15141923Baldwin339,800 lbs
1515 - 15191925Baldwin342,200 lbs
1520 - 15291926Baldwin360,890 lbs

Class Details by Steve Llanso of Sweat House Media

Class 4300 (Locobase 8652)

Data from 1947 and 1951 St L-SF locomotive diagram books supplied in May 2005 from the extensive collection of Allen Stanley.

Jim Quarles in a 1996 article entitled "Those Magnificent, Distinctive, Homebuilt, Frisco Mountains" (published on the web at, accessed 7 July 2007) says that this set of 11 engines was used to test the idea of rebuilding the never-satisfactory 2-10-2s into dual-service Mountains.(The more definitive conversions of 1939 -- the 4400 class -- are discussed in Locobase 224). 4300s used a cast frame and rode on Scullin disk drivers. Thermic syphons enriched the firebox heating surface in both the firebox itself and the combustion chamber. 14" piston valves admitted the steam to the cylinders.

According to Quarles, "They did have problems with the boilers cracking, because of a deficiency of the type of material specified for use in the boilers." He adds in the shops' defense: "Remember much of the advancements in metallurgy and technology during this period was being done by the railroads. The stresses and strains a boiler goes through are not trivial."

The Frisco nevertheless secured 15 years of useful work before dieselization rendered them redundant. The class was "dismissed from service" between 23 April 1952 and 20 October 1952.

Class 4400 (Locobase 224)

Data from 1947 and 1951 St L-SF locomotive diagram books supplied in May 2005 from the extensive collection of Allen Stanley.

Frisco rebuilds reusing all parts of earlier 2-10-2s (Locobase 8537) above the running gear. Oil-burners 4400-4412 pulled both freight and passenger trains; 4413-4422 burned coal and pulled freights only. Jim Quarles in a 1996 article entitled "Those Magnificent, Distinctive, Homebuilt, Frisco Mountains" (published on the web at, accessed 7 July 2007) argues that about all that was left of the 2-10-2 in the conversion was the original builder's plate.

The St Louis-San Francisco's 1947 locomotive diagram book shows that the firebox had 2 Nicholson thermic syphons of 76.2 sq ft in area and that the piston valves measured 15" in diameter. It also shows that 4407 & 4409 weighed considerably less on the drivers (278,850 lb). (Indeed, 4405-4409 had less superheating surface, their boilers holding only 54 flues but 245 tubes.)

The increases in heating surface and larger piston valves, together with the greater cylinder volume, made for more power at speed than the first set of conversions (see Locobase 8653 for the 4300s.)

Class T-54 (Locobase 223)

Data from table and diagram in 1930 Locomotive Cyclopedia and SL&SF 1930 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection and DeGolyer, Vol 74, pp. 335+. Works numbers were 56137 in January 1923; 56265-56278 in March; 58606-58610 in August 1925.

Firebox fitted with combustion chamber and thermic syphons. The boiler and firebox were very similar in size to that of Frisco 2-8-2s delivered by Baldwin in the same period. 1500-1514 burned oil fuel and used Baker valve gear. Steam was admitted through 14" (356 mm) piston valves. The combustion chamber contributed 95 sq ft (8.8 sq m) to direct heating surface.

Problems with the Baker gear (which were later cleared up, according to Don Wirth in January 1989 Railfan), led the Frisco to order the next five with Walschaerts gear in 1925 followed by the last ten, also with Walschaerts gear, 1926.

"Throughout their careers,"says Wirth, "...the 1500s were well liked by engine crews, dispatchers, and the motive power department. They were a true general-purpose locomotive, as well suited for use in hotshot freight service, fast passenger service, or even on the local." Some of their passenger runs were impressively long and included St Louis to Oklahoma City (542 miles/873 km) and Kansas City to Birmingham (737 miles/1,187 km) without engine change.

The last ten were completed to a different boiler and firebox design; see Locobase 15333.

Class T-54 (Locobase 15333)

Data from DeGolyer, Vol 74, pp. 373+. See also SL&SF 1947 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Works numbers were 59132-59134, 59169 in April 1926; 59198-59203 in May.

Locobase 223 describes the first twenty Baldwin Mountains that were delivered to the Frisco in 1923. The 1926 batch featured quite a few changes in the firebox and boilers. The firebox was fitted with combustion chamber and thermic syphons; the former contributed 89 sq ft (8.25 sq m) and the latter 84 sq ft (7.8 sq m). And the balance of tubes and flues shifted in favor of more large-diameter flues and, in this case at least, more superheater area.

Although these ten were delivered with Sellers injectors and were coal burners, but were shortly converted to oil firing with Chicago injectors.

The Frisco diagrams from 1947 show a superheating surface of 1,222 sq ft (113.5 sq m).

In either version, the 1500s were highly regarded by their crews and served the Frisco throughout the steam era.

Specifications by Steve Llanso of Sweat House Media
Locobase ID8652 224 223 15,333
RailroadSt Louis-San Francisco (Frisco/(SLSF)St Louis-San Francisco (Frisco/(SLSF)St Louis-San Francisco (Frisco/(SLSF)St Louis-San Francisco (Frisco/(SLSF)
Number in Class11232010
Road Numbers4300-43104400-44221500-15191520-1529
Number Built11232010
BuilderFriscoSt. Louis-San FranciscoBaldwinBaldwin
Valve GearWalschaertWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft)18.2518.251818
Engine Wheelbase (ft)42.3342.5040.3340.33
Ratio of driving wheelbase to overall engine wheebase 0.43 0.43 0.45 0.45
Overall Wheelbase (engine & tender) (ft)84.2385.9077.6077.60
Axle Loading (Maximum Weight per Axle) (lbs)70,63076,19063,450
Weight on Drivers (lbs)277,680298,800244,700247,000
Engine Weight (lbs)406,580449,760320,400355,000
Tender Loaded Weight (lbs)247,440255,890238,000240,500
Total Engine and Tender Weight (lbs)654,020705,650558,400595,500
Tender Water Capacity (gals)14,00014,00012,00011,700
Tender Fuel Capacity (oil/coal) (gals/tons)185000450017
Minimum weight of rail (calculated) (lb/yd)116125102103
Geometry Relating to Tractive Effort
Driver Diameter (in)70706969
Boiler Pressure (psi)250210200200
High Pressure Cylinders (dia x stroke) (in)27" x 30"29" x 32"28" x 28"28" x 28"
Tractive Effort (lbs)66,39168,62654,08554,085
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.18 4.35 4.52 4.57
Heating Ability
Firebox Area (sq ft)485410329405
Grate Area (sq ft)76.2076.2070.3070.30
Evaporative Heating Surface (sq ft)4720512243824440
Superheating Surface (sq ft)1834172611071180
Combined Heating Surface (sq ft)6554684854895620
Evaporative Heating Surface/Cylinder Volume237.42209.37219.59222.50
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation19,05016,00214,06014,060
Same as above plus superheater percentage24,38420,00316,87217,013
Same as above but substitute firebox area for grate area155,200107,62578,96098,010
Power L134,69922,74018,43019,692
Power MT1101.96671.13664.18703.05



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