Alaska Railroad 4-8-2 "Mountain" Locomotives in the USA

At 268,000 lbs, the Alaska Railroad Mountains were the lightest of the type.


CNRoad NumbersYear BuiltBuilder

Class Details by Steve Llanso of Sweat House Media

Class M-t/801 (Locobase 5094)

Data from [] (visited December 2002; later rvised as [], last accessed 6 May 2023); and [], last accessed 6 May 2023. (Thanks to Chris Hohl for his 4 April 2023 email noting the booster, variations in the heating surface areas.)

Small Mountain for this northernmost American railroad. Indeed, it is one of only three North American standard gauge 4-8-2s in Locobase with an adhesion weight under 200,000 lb. (90,719 kg).The others are the 1914 Canadian Pacific I1 class found in Locobase 4258 and the New Orleans Great Northern 200 at Locobase 6909).

Firebox had three thermic syphons (84 sq ft/7.80 sq m) and a combustion chamber (64 sq ft/5.95 sq m), which together contributed 148 sq ft (13.75 m) to the firebox heating surface area. Its Simplex Type BK mechanical stoker (first on the railroad) and the trailing truck booster were two prominent mod-cons.

Built at Eddystone, the engine was taken apart and shipped up to Anchorage, where they were reassembled in the shops. 801 (works number 61736 in May 1932) was completed in 1932. At the time of its delivery, Baldwin published a description of the 801. In later years, the ARR site prepared diagrams and data pages. Baldwin's report gave the count of 2 1/4" tubes as 192 and total heating surface area as shown at 2,991 sq ft. ARR's two diagrams specified 181 tubes and a total heating surface area as 2,870 sq ft (266.63 sqm)

Yet when Locobase used the 192 tube count in Baldwin's 1934 report, the tube area calculation generates a higher total evaporative heating surface area than the builder gives in the same report. Using the 181 count from the two diagrams, however, yields a nearly exact match.

It was wrecked twice, once in 1942,, which resulted in an extensive rebuild. and once in 1950.

802 (works number 64366) entered service on 5 December 1942 and ran until dieselization led to its retirement and scrapping in April 1954.

Principal Dimensions by Steve Llanso of Sweat House Media

Locobase ID5094
RailroadAlaska Railroad
Number in Class2
Road Numbers801-802
Number Built2
Valve GearBaker
Locomotive Length and Weight
Driver Wheelbase (ft / m)16.50 / 5.03
Engine Wheelbase (ft / m)38.50 / 11.73
Ratio of driving wheelbase to overall engine wheelbase 0.43
Overall Wheelbase (engine & tender) (ft / m)73.29 / 22.34
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)190,850 / 86,568
Engine Weight (lbs / kg)273,300 / 123,967
Tender Loaded Weight (lbs / kg)200,300 / 90,855
Total Engine and Tender Weight (lbs / kg)473,600 / 214,822
Tender Water Capacity (gals / ML)10,000 / 37.88
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)14 / 13
Minimum weight of rail (calculated) (lb/yd / kg/m)80 / 40
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)63 / 1600
Boiler Pressure (psi / kPa)220 / 15.20
High Pressure Cylinders (dia x stroke) (in / mm)22" x 30" / 559x762
Tractive Effort (lbs / kg)43,099 / 19549.40
Booster (lbs)11,800
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.43
Heating Ability
Tubes (number - dia) (in / mm)181 - 2" / 51
Flues (number - dia) (in / mm)32 - 5.375" / 137
Flue/Tube length (ft / m)18.50 / 5.64
Firebox Area (sq ft / m2)416 / 38.65
Grate Area (sq ft / m2)62.50 / 5.81
Evaporative Heating Surface (sq ft / m2)2991 / 277.87
Superheating Surface (sq ft / m2)706 / 65.59
Combined Heating Surface (sq ft / m2)3697 / 343.46
Evaporative Heating Surface/Cylinder Volume226.59
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation13,750
Same as above plus superheater percentage16,363
Same as above but substitute firebox area for grate area108,909
Power L119,994
Power MT923.85

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