Minneapolis, St Paul & Sault Ste Marie 4-8-2 "Mountain" Locomotives in the USA

The Minneapolis, St. Paul & Sault Ste. Marie Railway received ten updated versions of the USRA light (344,500 lbs) 4-8-2 locomotives from the American Locomotive Company in 1926. They were designated as Class N-20 and given road numbers 4000 through 4009. Eight more Class N-20 "Mountains", road numbers 4010 through 4017, came from ALCO in 1928.

Three more Class N-20 "Mountains", road numbers 4018 through 4020, were built by the MStP&SSM (Soo Line) in its Shoreham Shops in Minneapolis, MN.

All twenty-one of these Class N-20 "Mountains" had 27 x 30 cylinders, 69" drivers, and a boiler pressure of 200 psi which resulted in a tractive effort of 53,900 pounds.

There are no surviving Soo Line "Mountains".


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 N-20 (Locobase 226)

Data from table in 1930 Locomotive Cyclopedia and Soo 9 - 1943 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (Thanks to Chris Hohl for spotting the error in the valve gear.)

Updated versions of the USRA Mountain that, says Drury (1993), were meant to speed up freight service to offset the competitive disadvantages of a longer route between Chicago and Minneapolis that was single-tracked most of the way. Brooks produced the first 10, Schenectady the next 8, and the Soo itself the last 3.

Note that the superheater area in the specs is an estimate. It is a calculation based on taking the diagram value of 1,650 sq ft of "superheater equivalent" and deducting a third from it. See the logic presented in Locobase 1364. Also note that in this particular class, the 1,103 sq ft shown in the specs is taken directly from a 1930 Locomotive Cyclopedia table, which strengthens the case for the adjustment.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID226
RailroadMinneapolis, St Paul & Sault Ste Marie (Soo)
Number in Class21
Road Numbers4000-4020
Number Built21
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)18.25 / 5.56
Engine Wheelbase (ft / m)40.83 / 12.44
Ratio of driving wheelbase to overall engine wheebase 0.45
Overall Wheelbase (engine & tender) (ft / m)76.54 / 23.33
Axle Loading (Maximum Weight per Axle) (lbs / kg)57,900 / 26,263
Weight on Drivers (lbs / kg)231,500 / 105,007
Engine Weight (lbs / kg)342,000 / 155,129
Tender Loaded Weight (lbs / kg)171,800 / 77,927
Total Engine and Tender Weight (lbs / kg)513,800 / 233,056
Tender Water Capacity (gals / ML)12,000 / 45.45
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)17.50 / 15.90
Minimum weight of rail (calculated) (lb/yd / kg/m)96 / 48
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)69 / 1753
Boiler Pressure (psi / kPa)200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)27" x 30" / 686x762
Tractive Effort (lbs / kg)53,883 / 24440.95
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.30
Heating Ability
Firebox Area (sq ft / m2)341 / 31.69
Grate Area (sq ft / m2)70.30 / 6.53
Evaporative Heating Surface (sq ft / m2)3789 / 352.14
Superheating Surface (sq ft / m2)1103 / 102.51
Combined Heating Surface (sq ft / m2)4892 / 454.65
Evaporative Heating Surface/Cylinder Volume190.59
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation14,060
Same as above plus superheater percentage17,294
Same as above but substitute firebox area for grate area83,886
Power L117,841
Power MT679.61

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