Oregon Short Line / Union Pacific 4-8-0 "Mastodon" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class 900 (Locobase 3945)

A subsidiary of the Union Pacific, the OSL had several main lines out from western Wyoming into Idaho and Oregon. On the rugged grades of such terrain a low-drivered twelve-wheeler fit right in.

Data is taken from the Railroad Gazette of 9 March 1900. According to the RG for 20 April, one of these engines would pull a 1,650-1,700-ton train over a ruling grade of 0.9% from Pocatello to Dubois, where two Consolidations pushed from the rear to get the train up a 2 1/2% grade to Monida.

A compilation of Cooke locomotives by B.Rumary (25 Kingscombe, Gurney Slade, Radstock, BA3 4TH, ENGLAND) and supplied to Locobase by Allen Stanley in March 2004 shows the following works numbers:

2469-2471 (October 1899); road #900-903

2475 (October 1899); road #904

2495-2496 (November 1899); road #905-906

The class was vacated beginning in March 1926 (1854) and ending in November 1928 with 1853 and 1855.

Class Mastodon / TW-57 (Locobase 1224)

Data from an 1899 Brooks catalogue.

Brooks builder info from B.Rumary, 25 Kingscombe, Gurney Slade, Radstock, BA3 4TH, ENGLAND and Jeremy Lambert as supplied by Allen Stanley in March 2004. Works numbers 3211-3218 in May 1899. (Another seven 4-8-0s were classed as TW-55 and numbered 1850-1856.)

Illustration shows a high-mounted "Improved Belpaire" boiler with characteristic squared firebox (with 23 sq ft of arch pipes) and short funnel-shaped stack. Data from a Railroad Gazette article of 1900 (Vol XXXII, No. 18) shows slightly different grate and heating surface areas. Utah Rails points out that this class and the class of Ten-wheelers, were the only UP locomotives to have been fitted with Belpaire fireboxes.

Renumbered 1800-1807 later on. Retirements came in 1925 (1800-1804) and 1926 (1805-1807).

Specifications by Steve Llanso of Sweat House Media
Class900Mastodon / TW-57
Locobase ID3945 1224
RailroadOregon Short Line (UP)Union Pacific (UP)
Number in Class78
Road Numbers900-906 / 1850-18561500-1507 / 1800-1807
Number Built78
Valve GearStephensonStephenson
Locomotive Length and Weight
Driver Wheelbase (ft)15.6715.92
Engine Wheelbase (ft)26.2026.59
Ratio of driving wheelbase to overall engine wheebase 0.60 0.60
Overall Wheelbase (engine & tender) (ft)53.8853.85
Axle Loading (Maximum Weight per Axle) (lbs)42,750
Weight on Drivers (lbs)171,000163,000
Engine Weight (lbs)200,000197,000
Tender Loaded Weight (lbs)101,000106,000
Total Engine and Tender Weight (lbs)301,000303,000
Tender Water Capacity (gals)45005000
Tender Fuel Capacity (oil/coal) (gals/tons)1010.50
Minimum weight of rail (calculated) (lb/yd)7168
Geometry Relating to Tractive Effort
Driver Diameter (in)5557
Boiler Pressure (psi)200200
High Pressure Cylinders (dia x stroke) (in)21" x 30"21" x 30"
Tractive Effort (lbs)40,89339,458
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.18 4.13
Heating Ability
Firebox Area (sq ft)219231
Grate Area (sq ft)3334
Evaporative Heating Surface (sq ft)26762980
Superheating Surface (sq ft)
Combined Heating Surface (sq ft)26762980
Evaporative Heating Surface/Cylinder Volume222.51247.79
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation66006800
Same as above plus superheater percentage66006800
Same as above but substitute firebox area for grate area43,80046,200
Power L157496533
Power MT296.48353.44


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