Seaboard Air Line 4-8-2 "Mountain" Locomotives of the USA

The Seaboard Air Line Railroad receive its first ten "Mountains" (road numbers 200 through 209) the American Locomotive Company in 1914. These locomotives were designated as Class M and had 27 x 28 cylinders, 69" drivers, a boiler pressure of 190 psi, a tractive effort of 47,800 lbs and weighed 316,000 pounds. Another five (road numbers 210 through 214) arrived from ALCO in 1917 and were duplicates of the the earlier Class M. The "Mountains" were put to work in passenger service.

Ten more 4-8-2s (road numbers 215 through 224) were delivered from ALCO in 1922. These locomotives were designated as Class M-1 and were similar to those of Class M.

The SAL wanted more speed and ordered a total of 36 more "Mountains" with 72" drivers. These 4-8-2s were built by the Baldwin Locomotive Works and were delivered in three batches between 1924 and 1926. They had 27 x 28 cylinders, 72" drivers, and a boiler pressure of 200 psi which resulted in a tractive effort of 48,200 pounds.

All of the SAL "Mountains" were scrapped.

Roster by Richard Duley

ClassRoad NumbersYear BuiltBuilder
M200 - 2091914ALCO
M210 -2141917ALCO
M-1215 - 2241922ALCO
M-2225 - 2441924Baldwin
M-2245 - 2601925Baldwin
M-2261 - 2701926Baldwin

Class Details by Steve Llanso of Sweat House Media

Class M (Locobase 5008)

Much of the data comes from for 1929 locomotive diagrams. See also Railway Age Gazette (16 July 1915) and Railway Mechanical Engineer, January 1917.

The first group of Mountains built for the Richmond-Hamlet-Atlanta service. According to the Railway Age Gazette, the particular section assigned to this new class was challenging. In the 160 miles between Richmond to Raleigh NC, "... there are several grades of 1.2 per cent, 2 1/2 miles long; and from Raleigh to Columbia. 207 miles, on which there are grades of 1.25 per cent, 3 1/2 miles long."

RAG's comment on the reason for resorting to a 4-8-2 sounds very similar to French reasoning behind adopting 2-8-2s: "The introduction of the Mountain type engines was because of the inability of the locomotives of the Pacific type to maintain a sufficient speed up the grades with 10 or more steel cars to avoid the necessity of exceeding the maximum speed limit of 50 miles per hour on other parts of the run."

These were the only Seaboard Mountains with Walschaerts gear.

Firebox heating surface included 26 sq ft of arch tubes.

Superheat surface area originally was estimated from the calculation of the area of the flues and a calculated average ratio based on more that 350 locomotive entries in Locobase where both flue surface area and superheater areas are known. At the time, 857 sq ft seemed a close fit that likely slightly understated the real area. In fact, according to the table in the January 1917 issue of Railway Mechanical Engineer, the actual area was 865 sq ft. Not bad.

Class M-1 (Locobase 5007)

Much of the data comes from for 1929 locomotive diagrams. See Locobase 5008 for the first locomotives in this class

The second group of Mountains built for the Richmond-Hamlet-Atlanta service. They were a repeat of the first ten except for the substitution of Baker for Walschaert valve gear.

Firebox heating surface included 26 sq ft of arch tubes.

Class M-2 (Locobase 225)

Data from tables in Locomotive Cyclopedia of 1930 and SAL 1 - 1948 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. See also DeGolyer, Vol 75, pp. 258+. (Thanks to Chris Hohl for spotting the 16-gallon tender capacity originally entered and querying it.) Works numbers were 58074-58083 in November 1924; 58681- 58682 in September 1925; 58724-58728, 58748-58751, 58760-58764 in October; 58992-58996 in January 1926; 59047-59051 in March.

These were enlarged M-class Mountains (see Locobase 5008 and 5007) with a larger boiler holding eleven more superheater flues and a commensurately larger superheating surface. The firebox heating surface area expanded as well, but the same system of arch tubes contributed a similar 26 sq ft (2.4 sq m) to the overall value. Also, the combustion chamber length increased by almost 30% and now contributed 109 sq ft (10.1 sq m) to direct heating surface area.. Taken with the 3" taller drivers and the 14" (356 mm) piston valves, the result is a design that emphasized steaming capacity over tractive effort.

With this batch, the SAL had all of the Mountains it would want. They remained in service until 1956.

Specifications by Steve Llanso of Sweat House Media
Locobase ID5008 5007 225
RailroadSeaboard Air Line (SAL)Seaboard Air Line (SAL)Seaboard Air Line (SAL)
Number in Class101036
Road Numbers205-214215-224235-270
Number Built101036
Valve GearWalschaertBakerBaker
Locomotive Length and Weight
Driver Wheelbase (ft)181819.25
Engine Wheelbase (ft)38.9238.9240.66
Ratio of driving wheelbase to overall engine wheebase 0.46 0.46 0.47
Overall Wheelbase (engine & tender) (ft)76.3976.3178.38
Axle Loading (Maximum Weight per Axle) (lbs)52,90052,50053,250
Weight on Drivers (lbs)210,500209,000213,000
Engine Weight (lbs)316,000315,000320,500
Tender Loaded Weight (lbs)183,800183,800298,300
Total Engine and Tender Weight (lbs)499,800498,800618,800
Tender Water Capacity (gals)9000900016,000
Tender Fuel Capacity (oil/coal) (gals/tons)171720
Minimum weight of rail (calculated) (lb/yd)888789
Geometry Relating to Tractive Effort
Driver Diameter (in)696972
Boiler Pressure (psi)190190200
High Pressure Cylinders (dia x stroke) (in)27" x 28"27" x 28"27" x 28"
Tractive Effort (lbs)47,77647,77648,195
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.41 4.37 4.42
Heating Ability
Firebox Area (sq ft)319319343
Grate Area (sq ft)66.7066.7066.70
Evaporative Heating Surface (sq ft)371537154039
Superheating Surface (sq ft)8658651136
Combined Heating Surface (sq ft)458045805175
Evaporative Heating Surface/Cylinder Volume200.22200.22217.68
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation12,67312,67313,340
Same as above plus superheater percentage15,08115,08116,275
Same as above but substitute firebox area for grate area72,12672,12683,692
Power L115,42015,42020,667
Power MT645.99650.63855.64


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