Bangor & Aroostook 4-8-2 "Mountain" Locomotives in 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

ClassRoad NumbersYear BuiltBuilder
M100-1031929ALCO
M104-1061930ALCO
M107-1081935ALCO
M1091945ALCO

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 Rail Data Exchange. (Thanks to Chris Hohl for supplying the valve gear ID and for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error .Thanks also to Larry Walton for his 8 January 2021 email noting several corrections in the works numbers and build dates.) Works numbers were 68218-68221 in 1928 and 68525-68526, 68705-68706 in 1930. A ninth engine built to the same design was delivered as works number 73055 in February 1945.

Firebox had thermic syphons. Feed water heater was an Elesco A. 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). Of the ten in the class, nine had the same boiler and firebox. See Locobase 16524 for the 106, which used larger diameter tubes and flues.

Somehow the BAR managed to apply seven different classifications to them.


Class M-H (Locobase 16524)

Data from tables in 1930 Locomotive Cyclopedia and BAR 1 - 1938 Locomotive Diagrams supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection. (Thanks to Chris Hohl for supplying the valve gear ID and for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error; and to Leo Drake for his 26 February 2024 email pointing out a truncated comment.) Works number was 68527 in 1930.

Nine of the B&A's 4-8-2 freight class M used the same boiler. But in 1930, one more was delivered with larger-diameter small tubes (2 1/4" instead of 2") and flues (5 1/2" instead of 5 3/8"), leading to a 40-tube reduction in small tubes.

Locobase hasn't uncovered any explanation for why this engine, the last of the 1929 batch, was so modified.

Regardless of its differences, the 106 worked with the other eight until 1953, when it was scrapped.

Principal Dimensions by Steve Llanso of Middle Run Media
ClassMM-H
Locobase ID192 16524
RailroadBangor & AroostookBangor & Aroostook
CountryUSAUSA
Whyte4-8-24-8-2
Number in Class81
Road Numbers100-105, 107-108106
GaugeStdStd
Number Built81
BuilderAlco-SchenectadyAlco-Schenectady
Year19291930
Valve GearBakerBaker
Locomotive Length and Weight
Driver Wheelbase (ft / m)16.50 / 5.0316.50 / 5.03
Engine Wheelbase (ft / m)38.08 / 11.6138.08 / 11.61
Ratio of driving wheelbase to overall engine wheelbase 0.43 0.43
Overall Wheelbase (engine & tender) (ft / m)73.67 / 22.4576.71 / 23.38
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)213,360 / 96,779212,000 / 96,162
Engine Weight (lbs / kg)317,490 / 144,011315,300 / 143,018
Tender Loaded Weight (lbs / kg)232,000 / 105,234232,000 / 105,234
Total Engine and Tender Weight (lbs / kg)549,490 / 249,245547,300 / 248,252
Tender Water Capacity (gals / ML)10,000 / 37.8812,500 / 47.35
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)15 / 13.6018 / 16.40
Minimum weight of rail (calculated) (lb/yd / kg/m)89 / 44.5088 / 44
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)63 / 160063 / 1600
Boiler Pressure (psi / kPa)240 / 1650240 / 1650
High Pressure Cylinders (dia x stroke) (in / mm)22.5" x 30" / 572x76222.5" x 30" / 572x762
Tractive Effort (lbs / kg)49,179 / 22307.2549,179 / 22307.25
Booster (lbs)11,30011,300
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.34 4.31
Heating Ability
Tubes (number - dia) (in / mm)208 - 2" / 51168 - 2.25" / 57
Flues (number - dia) (in / mm)38 - 5.375" / 13738 - 5.5" / 140
Flue/Tube length (ft / m)20 / 6.1020 / 6.10
Firebox Area (sq ft / m2)351 / 32.61351 / 32.61
Grate Area (sq ft / m2)65.60 / 6.0965.60 / 6.09
Evaporative Heating Surface (sq ft / m2)3583 / 332.873424 / 318.10
Superheating Surface (sq ft / m2)932 / 86.58932 / 86.58
Combined Heating Surface (sq ft / m2)4515 / 419.454356 / 404.68
Evaporative Heating Surface/Cylinder Volume259.45247.94
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation15,74415,744
Same as above plus superheater percentage19,05019,050
Same as above but substitute firebox area for grate area101,930101,930
Power L125,04724,757
Power MT1035.231029.81

Photos

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