Boston & Maine Other Articulated Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class M-2-a (Locobase 6942)

Data from B&M Mechanical Department, Locomotives and Tenders Classification and Description dated 7 June 1928, supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange. See also B&G - UCCO Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange, from the Utah Rails site [] and, accessed 1 July 2005, and from Drury (1993). (Many thanks to Steve Low for his 4 December 2016 email pointing out a key error in boiler pressure for this engine and for adding several comments that helped Locobase revise this entry's with greater thoroughness and accuracy.) Works numbers were 63455-63456 in June 1922.

The firebox heating surface includes five arch tubes of 54 sq ft (5.02 sq m). HP cylinders admitted steam through 14" (356 mm) piston valves; the LP cylinders used slide valves.

In the east, about the only job for which these big all-adhesion Mallets were suited was yard switching and that's what the B&M wanted them to do.

After seven years of work at the Mechanicville hump yard, however, the B&M sold them to the Bingham & Garfield copper mining road in Utah in September 1929 as their 107-108. The later B&G diagram shows a reduction of 8 small tubes in the boiler for the 800, 13 for the 801. Arch tube area was recalculated as 60 sq ft (5.57 sq m). The changes aggregated to an evaporative heating surface area in the 800 of 5,215 sq ft (484.49 sq m) and 5,147 sq ft (478.17 sq m) in the 801.

Pressure setting rose to 230 psi ( 15.8 bar). Grate measurements remained the same, but the grate area measurement showed as 77 sq ft (7.15 sq m), the reduction possibly due to the adoption of a Rosebud grate (See Locobase 6941 for a longer description of the grate design.). New appliances included Alco's Type G power reverse gear, Elesco's Type CA1 feed water heater, and Elesco's Type HA superheater.

Engine weight grew to 474,100 lb (215,048 kg) and the engines now trailed tenders weighing 219,100 lb (99,382 kg). Water capacity increased to 12,000 US gallons (45,420 litres) and "slack" coal capacity amounted to 38,100 lb (17,282 kg).

801 received its last Class 3 overhaul in March 1947. 800's came a year later in March 1948. The B&G's operations ceased in April 1948 and the ICC approved its application to abandon the line in June. It's likely that the two locomotives were scrapped not long after.

(The Copperton low line, which began service on 1 April 1948, used electric locomotives. )

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID6942
RailroadBoston & Maine (B&M)
Number in Class2
Road Numbers800-801
Number Built2
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)14.75 / 4.50
Engine Wheelbase (ft / m)40.29 / 12.28
Ratio of driving wheelbase to overall engine wheebase 0.37
Overall Wheelbase (engine & tender) (ft / m)77.04 / 23.48
Axle Loading (Maximum Weight per Axle) (lbs / kg)59,600 / 27,034
Weight on Drivers (lbs / kg)465,000 / 210,921
Engine Weight (lbs / kg)474,100 / 215,048
Tender Loaded Weight (lbs / kg)189,500 / 85,956
Total Engine and Tender Weight (lbs / kg)663,600 / 301,004
Tender Water Capacity (gals / ML)11,000 / 41.67
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)13 / 11.80
Minimum weight of rail (calculated) (lb/yd / kg/m)97 / 48.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)51 / 1295
Boiler Pressure (psi / kPa)220 / 15.20
High Pressure Cylinders (dia x stroke) (in / mm)26" x 28" / 660x711
Low Pressure Cylinders (dia x stroke) (in / mm)40" x 28" / 1016x711
Tractive Effort (lbs / kg)97,578 / 44260.69
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.77
Heating Ability
Firebox Area (sq ft / m2)371 / 34.47
Grate Area (sq ft / m2)80.30 / 7.46
Evaporative Heating Surface (sq ft / m2)5298 / 492.20
Superheating Surface (sq ft / m2)1367 / 127
Combined Heating Surface (sq ft / m2)6665 / 619.20
Evaporative Heating Surface/Cylinder Volume307.92
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation17,666
Same as above plus superheater percentage21,376
Same as above but substitute firebox area for grate area98,760
Power L18934
Power MT338.86

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