Baltimore & Ohio 2-8-8-4 "Yellowstone" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class EM-1 (Locobase 333)

Data from tables and diagrams in 1947 Locomotive Cyclopedia and B&O to 1954 Asstd Loco Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Works numbers were 70062-70081 (1943) and 71502-71511 (1945).

Firebox heating surface included 211 sq ft (19.6 sq m) of five thermic syphons and arch tubes; the long combustion chamber added considerable area as well. Lateral cushioning devices on each lead driver axle eased the locomotive into curves; the lead axle in the trailing truck also had one. Every axle on the engine and tender turned with roller bearings, which significantly reduced friction, the boiler's water came through Worthington feedwater heaters, coal appeared on the enormous grate from an HT-M automatic stoker, and 12" (305 mm) piston valves supplied steam to each of the four cylinders.

Drury (1993) says that "they were truly modern locomotives -- and they weren't what B&O wanted. The EM-1s probably wouldn't have been built but for the restrictions on diesels imposed by the War Production Board." On the other hand, they were very highly regarded engines that were the heaviest to be bought by the B&O, but among the lightest super-sized articulateds to be produced. They were, in fact almost 20 tons lighter on the drivers than the next heaviest engine (the Espee's AC-9 backup).

Despite the B&O's initially cool reception, the EM-1s soon established themselves as one of the premier articulateds in the East. In their initial assignments on the Cumberland and Pittsburgh Divisions and later on the ore-boat shuttles in northern Ohio, they proved powerful, quite reliable, and fast enough even to work an occasional passenger train. One less-obvious reason for this success was the relatively low boiler pressure setting, which raised the factor of adhesion. Some of the heavier coal and ore trains needed two EM-1s on the point and a third as pusher on the rear.

As dieselization progressed, the EM-1s were sidelined, being reawakened in several years to pick up the slack during times of heavy freight volume. The last retired in 1960.

Specifications by Steve Llanso of Sweat House Media
Locobase ID333
RailroadBaltimore & Ohio (B&O)
Number in Class30
Road Numbers7600-7629
Number Built30
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase16.50'
Engine Wheelbase65.17'
Ratio of driving wheelbase to overall engine wheebase 0.25
Overall Wheelbase (engine & tender)112.50'
Axle Loading (Maximum Weight per Axle)62100 lbs
Weight on Drivers485000 lbs
Engine Weight628700 lbs
Tender Light Weight382000 lbs
Total Engine and Tender Weight1010700 lbs
Tender Water Capacity22000 gals
Tender Fuel Capacity (oil/coal)25 tons
Minimum weight of rail (calculated)101 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter64"
Boiler Pressure235 psi
Cylinders (dia x stroke)24" x 32"
Tractive Effort115056 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.22
Heating Ability
Firebox Area756 sq. ft
Grate Area117.50 sq. ft
Evaporative Heating Surface5298 sq. ft
Superheating Surface2118 sq. ft
Combined Heating Surface7416 sq. ft
Evaporative Heating Surface/Cylinder Volume158.10
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation27613
Same as above plus superheater percentage35620
Same as above but substitute firebox area for grate area229181
Power L121050
Power MT765.48



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