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 53,883 pounds. They were also equiped with trailing truck boosters which provided an additional 11,800 lbs of tractive effort resulting in a total starting TE of over 65,000 lbs.

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 and for his 2 April 2021 email supplying builder's cards B-1689 and S-1622, correcting the original 1st built date, and providing in detail the tender changes described below.) Brooks's works numbers were 67119-67128 in November 1926. Schenectady followed with works numbers 67614-67621 in June 1928.

Updated versions of the USRA Mountain (Locobase 231) 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.

Brooks's decade of engines, Hohl noted, came with tenders that carried 16 tons of coal and 10,000 US gallons (37,850 litres), weighed 192,500 lbs (87,317 kg)., and contributed to a total wheelbase of 75' 6½" (23.02 m). Schenectady's eight had larger tenders that carried the same amount of coal, but increased water capacity to 12,000 gallons. Overall wheelbase increased 12" to 76' 6 1/2" (23.33 m).

Locobase noted two discrepancies between the N-20 builders' data. All locomotives had boosters, but Brooks's installation was credited with 11,800 lb (5,352 kg) of starting tractive effore; Schenectady's setup generated 10,720 lb (4,863 kg). Also, Brooks calculated the boiler's superheated surface area as 1,162 sq ft (107.95 sq m); Schenectady's figure was 1,103 sq ft (102.47 sq m).

Locobase thinks it's fitting that he quote Hohl's account of the latter-day tender changes his research laid out:

"The original tenders appear to have been increased to carry 17½ tons / 12,000 gallons by 1930, the revised tender weight [rose to] 216,000 lbs [97,976 kg]. (#4000-4017), and the total wheelbase increased [9 more inches] to 77' 3½" (23.56 m]

"[Soo-built] 4018-4020 had slightly lower weights than the ALCO-built ones (D[rivers]: 227,500 lbs [103.192 kg] | E[ngine]: 338,700 lbs [153,224 kg],| T[ender]: 210,400 lbs [95,436 kg].)....still later, #4000-4005, #4007-4015, & #4017 later had their tenders swapped out for larger, shop-built tenders that carried 22 tons [20 metric tons] /18,000 gallons [68,130 litres] and weighed 328,000 lbs. (which also increased their total wheelbase to 82' 7¾"), and they also had an increase in their engine weight (from their leading trucks) of 3,000 lbs [1,361 kg]"

Hohl cites {1930 Locomotive Cyclopedia | pages 115 & 231, 1938 Locomotive Cyclopedia | page 202, 1930 SOO diagram book | pages 101-102, & 116/116, 1942 SOO diagram book | page 52/55, and Soo Line 4-8-2 builders cards}.

[Original note: "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
BuilderAlco - multiple works
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 wheelbase 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 / Liters/MT)17.50 / 16
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
Booster (lbs)10,800
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.30
Heating Ability
Tubes (number - dia) (in / mm)184 - 2.25" / 57
Flues (number - dia) (in / mm)45 - 5.5" / 140
Flue/Tube length (ft / m)20 / 6.10
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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