Bangor & Aroostook 4-8-2 "Mountain" Locomotives of the USA

The Bangor & Aroostook Railroad took delivery of four "Mountain" locomotives (road numbers 100 through 103) in 1929 and three more (road numbers 104 through 106) in 1930. Three more would follow: two (road numbers 107 & 108) in 1935 and the last one (road number 109) in 1945. All ten of these locomotives were designated Class M and were built by the American Locomotive Company.

The BAR "Mountains" had 22.5 x 30 cylinders, 63" drivers, a 240 psi boiler pressure which resulted in a tractive effort of 50,000 pounds. The weight on the drivers was 214,500 lbs and the total weight for each locomotive was 318,500 lbs. With a full load of 12,000 gallons of water and 18 tons of coal the combined weight of the locomotive and tender was 551,500 pounds.

The BAR also purchased five used "Mountains" from the NYO&W in 1946 and scrapped them by 1949. The ten from ALCO were retired by 1953. There are no survivors.

Roster by Richard Duley

ClassRoad NumbersYear BuiltBuilder

Class Details by Steve Llanso of Sweat House Media

Class M (Locobase 192)

Data from tables in 1930 Locomotive Cyclopedia and BAR 7 - 1951 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. (Thanks to Chris Hohl for supplying the valve gear ID.) Works numbers were 68218-68221 in 1928 and 68525-68527, 68705-68706 in 1930.

Firebox had thermic syphons. Relatively small Mountain types with small drivers for low-speed freight hauling. Originally listed weight on the drivers came to 204,000 lb (92,533 kg). All ten had the same boiler and firebox.

Somehow the BAR managed to apply seven different classifications to them. 106 received its M-H subclass designation when the shops removed 40 small tubes from its boiler. Tube heating surface area dropped by 159 sq ft (14.75 sq m), which reduced total evaporative heating surface area to 3,424 sq ft (318.1 sq m).

Specifications by Steve Llanso of Sweat House Media
Locobase ID192
RailroadBangor & Aroostook
Number in Class10
Road Numbers100-109
Number Built10
Valve GearBaker
Locomotive Length and Weight
Driver Wheelbase16.50'
Engine Wheelbase38.08'
Ratio of driving wheelbase to overall engine wheebase 0.43
Overall Wheelbase (engine & tender)73.67'
Axle Loading (Maximum Weight per Axle)
Weight on Drivers213360 lbs
Engine Weight317490 lbs
Tender Light Weight232000 lbs
Total Engine and Tender Weight549490 lbs
Tender Water Capacity10000 gals
Tender Fuel Capacity (oil/coal)15 tons
Minimum weight of rail (calculated)89 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter62"
Boiler Pressure240 psi
Cylinders (dia x stroke)22.5" x 30"
Tractive Effort49972 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.27
Heating Ability
Firebox Area351 sq. ft
Grate Area65.60 sq. ft
Evaporative Heating Surface3583 sq. ft
Superheating Surface932 sq. ft
Combined Heating Surface4515 sq. ft
Evaporative Heating Surface/Cylinder Volume259.53
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation15744
Same as above plus superheater percentage19050
Same as above but substitute firebox area for grate area101930
Power L124657
Power MT1019.11


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