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


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 seven engines were substantially rebuilt. 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 "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.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID16,176
RailroadSt Louis Southwestern (Cotton Belt)
Number in Class7
Road Numbers680-686
Number Built
Valve GearBaker
Locomotive Length and Weight
Driver Wheelbase (ft / m)19.83 / 6.04
Engine Wheelbase (ft / m)41 / 12.50
Ratio of driving wheelbase to overall engine wheebase 0.48
Overall Wheelbase (engine & tender) (ft / m)79.08 / 24.10
Axle Loading (Maximum Weight per Axle) (lbs / kg)63,800 / 28,939
Weight on Drivers (lbs / kg)253,400 / 114,940
Engine Weight (lbs / kg)365,000 / 165,561
Tender Loaded Weight (lbs / kg)202,850 / 92,011
Total Engine and Tender Weight (lbs / kg)567,850 / 257,572
Tender Water Capacity (gals / ML)11,000 / 41.67
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)3700 / 14
Minimum weight of rail (calculated) (lb/yd / kg/m)106 / 53
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)74 / 1880
Boiler Pressure (psi / kPa)220 / 15.20
High Pressure Cylinders (dia x stroke) (in / mm)26.5" x 28" / 673x711
Tractive Effort (lbs / kg)49,689 / 22538.58
Factor of Adhesion (Weight on Drivers/Tractive Effort) 5.10
Heating Ability
Firebox Area (sq ft / m2)360 / 33.44
Grate Area (sq ft / m2)63 / 5.85
Evaporative Heating Surface (sq ft / m2)4646 / 431.62
Superheating Surface (sq ft / m2)1196 / 111.11
Combined Heating Surface (sq ft / m2)5842 / 542.73
Evaporative Heating Surface/Cylinder Volume259.93
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation13,860
Same as above plus superheater percentage16,632
Same as above but substitute firebox area for grate area95,040
Power L126,125
Power MT909.17

All material Copyright ©
Wes Barris