Minneapolis, St Paul & Sault Ste Marie 4-8-4 "Northern" Locomotives in the USA

The Minneapolis, St. Paul & Sault Sainte Marie Railroad purchased four Class O-20, 4-8-4s in 1938 from the Lima Locomotive Works. They were given road numbers 5000 through 5003 and were assigned to both freight and passenger trains.

These locomotives were designed with 75" drivers, 26 x 32 cylinders, a 270 psi boiler pressure, a weight of 445,550 pounds and had a tractive effort of 66,000 pounds.

There are no survivors.


ClassQtyRoad NumbersLocomotive WeightYear BuiltBuilder
N-20 104000-4009344,500 lbs1926ALCO
N-2084010-4017342,000 lbs1928ALCO
N-2034018-4020338,700 lbs1930Soo

Class Details by Steve Llanso of Sweat House Media

Class O-20 (Locobase 278)

Data from Soo 1942 Locomotive Diagrams supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange. See also Negative Order No. 1145, Lima Locomotive Works, Incorporated builder card supplied by Chris Hohl in his 3 January 2018 email pointing out the correct boiler pressure of 270 psi. Works numbers were 7753-7756 in January 1938.

Classic Northern from the late 1930s that carried its boiler and firebox on an frame that was integrally cast with both the cylinders and the air reservoirs. Piston valves measured a modest 12" (306 mm) in diameter. The Elesco Type E superheater included a dryer. In place of the commonly adopted feed water heaters, the O-20s used an Elesco Type SL-305 exhaust steam injector. The 1942 Soo diagram shows the combustion chamber, but doesn't show its heating surface area. The builder's card reported 47 sq ft (4.37 sq m) in arch tubes. Although the negative gave the engine weight as 445,550 lb (202,098 kg), later diagrams reflected greater weight on the trailing truck.

Drury (1993) says of these engines: "Assigned to fast Chicago-Twin Cities freight trains, [they] acquired a reputation for availability -- they were able to turn at the terminals and be on their way quickly." Each locomotive averaged 100,000 miles (161,000 km) per year.

Dieselization shortened the quartet's careers and all four were sold for scrap in December 1954.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID278
RailroadMinneapolis, St Paul & Sault Ste Marie (Soo)
Number in Class4
Road Numbers5000-5003
Number Built4
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)19.75 / 6.02
Engine Wheelbase (ft / m)46.75 / 14.25
Ratio of driving wheelbase to overall engine wheebase 0.42
Overall Wheelbase (engine & tender) (ft / m)87.79 / 26.76
Axle Loading (Maximum Weight per Axle) (lbs / kg)65,900 / 29,892
Weight on Drivers (lbs / kg)263,000 / 119,295
Engine Weight (lbs / kg)453,500 / 205,704
Tender Loaded Weight (lbs / kg)317,600 / 144,061
Total Engine and Tender Weight (lbs / kg)771,100 / 349,765
Tender Water Capacity (gals / ML)17,500 / 66.29
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)24 / 21.80
Minimum weight of rail (calculated) (lb/yd / kg/m)110 / 55
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)75 / 1905
Boiler Pressure (psi / kPa)270 / 18.60
High Pressure Cylinders (dia x stroke) (in / mm)26" x 32" / 660x813
Tractive Effort (lbs / kg)66,194 / 30025.13
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.97
Heating Ability
Firebox Area (sq ft / m2)423 / 39.30
Grate Area (sq ft / m2)88.30 / 8.20
Evaporative Heating Surface (sq ft / m2)5142 / 477.70
Superheating Surface (sq ft / m2)2120 / 196.95
Combined Heating Surface (sq ft / m2)7262 / 674.65
Evaporative Heating Surface/Cylinder Volume261.49
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation23,841
Same as above plus superheater percentage30,755
Same as above but substitute firebox area for grate area147,331
Power L145,203
Power MT1515.67

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