Boston & Maine 4-8-2 "Mountain" Locomotives of the USA

The Boston & Maine Railroad's last purchase of steam locomotives was its Class R-1 "Mountains" built by the Baldwin Locomotive Works. These eighteen 4-8-2s (road number 4100 through 4117) each weighed 416,100 lbs and were some of the heaviest 4-8-2s built in the United States. They had 28 x 31 cylinders, 73" drivers, a 240 psi boiler pressure and a tractive effort of 67,900 pounds.

Each of the B&M "Mountains" carried a name in addition to its road number. These names were selected from contest entries and were assigned as noted below.

Thirteen of these locomotives (road numbers 4100 through 4112) were sold to the B&O in 1947 and the remaining five were retired in 1955 and 1956 and were scrapped shortly after.

Class Details by Steve Llanso of Sweat House Media

Class R-1 (Locobase 4410)

Data from 1947 Boston & Maine Description of Locomotives supplied in May 2005 by Allen Stanley from his extensive Raildata collection. (Thanks to Chris Hohl for his 26 February 2016 email supplying the locomotive negative and specification cards found at SMU's DeGolyer Library's image collection: R-1a,; R-1b,; and R-1d, . Also thanks for a later email noting the misplacement of 4105 in the wrong subclass.)

There were four R-1 classes comprising eighteen engines -- all were named in contests. All had integral cast-steel beds, 14" (356 mm) piston valves. R-1a used spoked wheels on all driving axles and had the safety valve stand located just ahead of the cab. R-1b had Baldwin discs on the main driven axle, and R-1ds had Baldwin discs on all driving axles. Safety valves were relocated in the last three subclasses to a mid-boiler position between the small steam dome and large sand dome

These first thirteen were delivered with Coffin size C-85 feedwater heaters. The R-1ds used Worthington 5-SAs.

The first three subclasses trailed twelve-wheel tenders on two three-axle trucks, each wheel of 36" (914 mm) diameter; tender wheelbase came to 36 ft 1 in (11 m). They carried 20,000 US gallons (75,700 litres) of water and 21 tons of coal when delivered. They weighed about 369,000 lb (167,376 kg) loaded. Later, they used larger tenders, still rolling on two six-wheel trucks, that held a bit more water and 2 1/2 tons more coal. These are shown in the Locobase specs above.

R-1d tenders had fourteen larger (42") wheels that were carried in three two-axle trucks and a single trailing truck, an arrangement that reduced the tender's wheelbase to 32 ft 8 in (9.96 m) . Fuel capacity stayed at 21 tons, but water capacity increased to 23,000 gallons (87,055 litres). Tender weight increased to 399,600 lb (181,256 kg).

R-1a (1935) works numbers 61822-61826. Loaded weight was 416,100 lb.

4100 Endurance

4101 Hannah Dustin

4102 Cardigan

4103 Oliver Wendell Holmes

4104 Bee & Emma

R-1b (1937) works numbers 62033-62037. Loaded weight was 416,100 lb.

4105 Powwow River

4106 Little John

4107 Intrepid

4108 Lily Pons

4109 Bumble Bee

R-1c (1939) works numbers 62318-62319, 6232. Loaded weight 414,960 lb.

4110 Calvin Coolidge

4111 Trojan

4112 Swallow

R-1d (1941) works numbers 62536-62540; weighed 415,200 lb.

4113 Black Arrow

4114 Invincible

4115 Casey Jones

4116 American Progress

4117 Hercules

4100-4112 were sold to the B&O in 1947as T-4 class 5650-5612 as the B&M dieselized. The last 5 remained in B & M service until 1955-1956.

Specifications by Steve Llanso of Sweat House Media
Locobase ID4410
RailroadBoston & Maine (B&M)
Number in Class18
Road Numbers4100-4117
Number Built18
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase19.25'
Engine Wheelbase44.17'
Ratio of driving wheelbase to overall engine wheebase 0.44
Overall Wheelbase (engine & tender)92.67'
Axle Loading (Maximum Weight per Axle)68900 lbs
Weight on Drivers269400 lbs
Engine Weight416100 lbs
Tender Light Weight372700 lbs
Total Engine and Tender Weight788800 lbs
Tender Water Capacity20200 gals
Tender Fuel Capacity (oil/coal)22.5 tons
Minimum weight of rail (calculated)112 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter73"
Boiler Pressure240 psi
Cylinders (dia x stroke)28" x 31"
Tractive Effort67918 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.97
Heating Ability
Firebox Area475 sq. ft
Grate Area79 sq. ft
Evaporative Heating Surface4511 sq. ft
Superheating Surface1924 sq. ft
Combined Heating Surface6435 sq. ft
Evaporative Heating Surface/Cylinder Volume204.18
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation18960
Same as above plus superheater percentage24648
Same as above but substitute firebox area for grate area148200
Power L131987
Power MT1047.06



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