St Louis Southwestern 4-8-2 "Mountain" Locomotives in the USA


Roster

ClassRoad NumbersBuilderPrevious Owner
L0675 - 679ALCO (Schenectady)FEC (Locobase 1348)
M1680 - 686ALCO (Brooks)
L1800 - 819Baldwin / SLSW

Class Details by Steve Llanso of Sweat House Media

Class M1 (Locobase 16176)

Data from StL&SW 1 - 1945 Folio 725 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.This entry exists because Chris Hohl sent an email on 30 January 2016 noting the many significant differences between the Rock Island's M-50 class and the seven engines rebuilt by the Cotton Belt after they purchased the septet in May 1941 and suggesting they deserved an entry of their own.

When the Rock sold off some of their 4-8-2s, they sent seven of the earlier batch. These had received few changes during their time on the Rock Island. In particular, 4006-4007 and 4015 left for the Cotton Belt as coal burners. Locobase believes that 4033-4023, 4028, and 4031 were delivered in 1924 as oil burners. All still used 16" (406 mm) piston valves and included three thermic syphons in their fireboxes.

Almost as soon as they arrived on the St Louis-Southwestern, the shops substantially rebuilt the seven engines. As with the later M-50s described in Locobase 201, the 880s lost one of the three thermic syphons, which reduced to 82 sq ft (7.62 sq m) the component's contribution to firebox heating surface area. The three coal burners were converted to oil-burning and all trailed tenders with slight greater oil capacity than those of the Rock Island.

Although they retained the orginal count of tubes and superheater flues, the 880s raised boiler pressure to 220 psi to compensate for a 1 1/2" (38 mm) cylinder diameter reduction.that was now served by 14" (356 mm) piston valves. The alligator crossheads was replaced by multiple-bearing crossheads. The 1945 diagram shows that four of the engines--680-682, 686--were later fitted with Alco reverse gear using "allservice" poppet valves.

Like the M-50a, the drivers were disc type and all engine axles turned in Timken roller bearings.

The seven also changed service, pulling only fast freights for the twelve years they ran on the Cotton Belt. All were sold for scrap in August 1953.


Class Proposed (Locobase 16450)

Data from Baldwin proposal 7859 reproduced in Joseph A Strapac, Cotton Belt Locomotives (Huntington Beach, Calif. : Shade Tree Books, 1977), p. 116. (Many thanks to Chris Hohl, whose 10 September 2019 email told Locobase of the design and supplied the diagram. His comments on the design are repeated below. Hohl also spelled out the Cotton Belt's two 4-8-2 classes.)

Chris Hohl's analysis revealed the many similarities between this design and the P-2 Mountains Eddystone delivered to the Great Northern in 1923 (Locobase 206). "The driving & engine wheelbases would have been a match, as well as the tender capacities, driver diameter, cylinders, boiler pressure, superheater surface area, and valve gear. The SSW's 4-8-2s would have been heavier (both locomotive and tender), and the firebox heating surface area would have been higher. However, their total wheelbase would have been slightly shorter, and both the grate area and evaporative heating surface area would have been smaller."

The greater firebox heating surface area included 95 sq ft (8.83 sq m) from the combustion chamber, 70 (6.50 sq m) from the thermic syphons, and 24 (2.23 sq m) from arch tubes. Like the GN P-2, the proposed SSW Mountain would have had over-square cylinders in which the cylinder diameter is greater than the stroke. Locobase asked his database what it would have taken to match the tractive effort supplied by an over-square 29 x 28 if the diameter were 28. A 28 x 30 cylinder had the same volume, but piston speed at the same locomotive speed would have been 7% higher.

The Cotton Belt did not buy any Mountain locomotives at this time. Hohl observed that the StL&SW procured their first 4-8-2s from the Florida East Coast in 1937; they took numbers 675;-679 and formed class L-0. Seven more 4-8-2s were rebuilds of Rock Island engines in 1941 (Locobase 16176), which the Cotton Belt rebuilt.

Principal Dimensions by Steve Llanso of Sweat House Media

ClassM1Proposed
Locobase ID16176 16450
RailroadSt Louis Southwestern (Cotton Belt)St Louis Southwestern (Cotton Belt)
CountryUSAUSA
Whyte4-8-24-8-2
Number in Class7
Road Numbers680-686
GaugeStdStd
Number Built
BuilderSSWBaldwin
Year19411927
Valve GearBakerWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)19.83 / 6.0419 / 5.79
Engine Wheelbase (ft / m)41 / 12.5041.58 / 12.67
Ratio of driving wheelbase to overall engine wheelbase 0.48 0.46
Overall Wheelbase (engine & tender) (ft / m)79.08 / 24.1081.50 / 24.84
Axle Loading (Maximum Weight per Axle) (lbs / kg)63,800 / 28,939
Weight on Drivers (lbs / kg)253,400 / 114,940258,000 / 117,027
Engine Weight (lbs / kg)365,000 / 165,561378,000 / 171,458
Tender Loaded Weight (lbs / kg)202,850 / 92,011253,000 / 114,759
Total Engine and Tender Weight (lbs / kg)567,850 / 257,572631,000 / 286,217
Tender Water Capacity (gals / ML)11,000 / 41.6712 / 0.05
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)3700 / 14,0055000 / 18,925
Minimum weight of rail (calculated) (lb/yd / kg/m)106 / 53108 / 54
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)74 / 188072 / 1829
Boiler Pressure (psi / kPa)220 / 15.20200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)26.5" x 28" / 673x71129" x 28" / 737x711
Tractive Effort (lbs / kg)49,689 / 22538.5855,599 / 25219.31
Factor of Adhesion (Weight on Drivers/Tractive Effort) 5.10 4.64
Heating Ability
Tubes (number - dia) (in / mm)216 - 2.25" / 57194 - 2.25" / 57
Flues (number - dia) (in / mm)45 - 5.5" / 14050 - 5.5" / 140
Flue/Tube length (ft / m)22.42 / 6.8322 / 6.71
Firebox Area (sq ft / m2)360 / 33.45452 / 41.99
Grate Area (sq ft / m2)63 / 5.8685 / 7.90
Evaporative Heating Surface (sq ft / m2)4646 / 431.784533 / 421.28
Superheating Surface (sq ft / m2)1196 / 111.151368 / 127.14
Combined Heating Surface (sq ft / m2)5842 / 542.935901 / 548.42
Evaporative Heating Surface/Cylinder Volume259.99211.72
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation13,86017,000
Same as above plus superheater percentage16,63220,910
Same as above but substitute firebox area for grate area95,040111,192
Power L126,13121,416
Power MT909.38732.00

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