Atlantic & Pacific 4-8-0 "Mastodon" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class 26/631 (Locobase 8996)

Data from AT&SF 9 -1920 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also "Large Locomotives for the West", Locmotive Engineers' Monthly Journal, Vol 15, No 10 (October 1881), p. 445; and George B Abdill, A Locomotive Engineer's Album (Seattle: Superior Publishing Company, 1965), p. 138.. Information about how many, when, and by whom this class was supplied from (accessed 6 Feb 2006), the Santa Fe All-Time Steam Roster maintained by Evan Werkema. Additional roster information from the Al WeberRail Data Exchange supplied by Allen Stanley in August 2013. Works numbers were 993-1002 in July 1881.

Interesting Twelve-wheelers that were described by the LEMJ report as "monster locomotives" when they were shipped off to New Mexico. An awestruck commentator added that "The tops of the cabs of these locomotives are higher than the smoke-stacks used on Eastern railroads ...The great size and weight of the engines are made necessary by the heavy grades they will have to overcome."

George Abdill noted that the firebox extended through the cab to the back edge of the footplate. The engineer and fireman were separated, but the latter individual spent most of his time out on the open deck, bailing black diamonds into her long, narrow firebox." The 1920 Santa Fe diagram shows that even then the smokestack was topped by a truncated funnel that conatined a spark arrestor.

They were renumbered in 1882 as 19-27. On 11 January 1887, 27 suffered a boiler explosion and was scrapped. The rest of the class was taken into the Santa Fe Pacific in 1897 with the same numbers, renumbered in 1898 as 237-245. When the SFP's parent Santa Fe renumbered them in 1902, they broke the series into 637-639, 631-635 respectively.

Most were retired and scrapped from the Santa Fe from 1907 to 1917, but the 633 was sold to the Belington & Beaver Creek as their #77 in 1902. In 1905, Western Maryland took over the B&BC and renumbered the 77 as their 252. The locomotive was retired from that railway in December 1908.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID8996
RailroadAtlantic & Pacific (ATSF)
Number in Class10
Road Numbers26-35/631-639
Number Built10
BuilderRhode Island
Valve GearStephenson
Locomotive Length and Weight
Driver Wheelbase (ft / m)15 / 4.57
Engine Wheelbase (ft / m)25.50 / 7.77
Ratio of driving wheelbase to overall engine wheebase 0.59
Overall Wheelbase (engine & tender) (ft / m)49.83 / 15.19
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)109,450 / 49,646
Engine Weight (lbs / kg)129,200 / 58,604
Tender Loaded Weight (lbs / kg)64,900 / 29,438
Total Engine and Tender Weight (lbs / kg)194,100 / 88,042
Tender Water Capacity (gals / ML)4000 / 15.15
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)8 / 7.30
Minimum weight of rail (calculated) (lb/yd / kg/m)46 / 23
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)53 / 1346
Boiler Pressure (psi / kPa)150 / 10.30
High Pressure Cylinders (dia x stroke) (in / mm)20" x 26" / 508x660
Tractive Effort (lbs / kg)25,019 / 11348.44
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.37
Heating Ability
Firebox Area (sq ft / m2)161 / 14.96
Grate Area (sq ft / m2)35 / 3.25
Evaporative Heating Surface (sq ft / m2)1738 / 161.52
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)1738 / 161.52
Evaporative Heating Surface/Cylinder Volume183.84
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation5250
Same as above plus superheater percentage5250
Same as above but substitute firebox area for grate area24,150
Power L13564
Power MT287.15

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Wes Barris