Saint Louis, Iron Mountain & Southern 2-8-8-2 "Chesapeake" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class ML-55 (Locobase 10031)

Data from William Ernest Dalby, Steam Power (London: Longmans, Green, and Co., 1915), p. 269, supplemented by Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University, Volume 40, pp. 138-149 and from "MoPac 2-8-8-2 No. 4000 "Molly" the Mallet -

The Mightiest of them All," T Greuter ( Works number was 37675

in April 1912.

A pretty large fish out of water, this single Mallet's boiler included 1,230 sq ft of feedwater heater. When 4000 arrived on the railroad, it almost immediately acquired a nickname - Molly - which reflected both the tendency of engine crews to think of their locomotives as iron women and a probable play on the usual pronunciation of Mallet ("Malley").

Molly ran on the StL & IM and the Missouri Pacific as a hump switcher until 1946. T. Greuter, writing on the Trainweb website, offered an affectionate description of Molly's career. First he tells us what she didn't do: "It is easy to imagine that such an impressive engine as Molly may have been put to use on the most powerful runs of the day, cresting the limestone rises of Kirkwood with a mile-long line of coal freight, but she didn't."

So, a grand vision, yes, but not what she did, as Greuter explains:

"The fact is Molly was a blue-collar worker, through and through. Her sheer massiveness made her ideally suited for effortlessly shuffling the high tonnage in endless strings of cars, breaking-up and building trains at Missouri Pacific's yard hump in St. Louis and Dupo, as well as tending transfer drags ... a sight that must have truely been awe inspiring to witness."

And, he notes, "Nothing else owned by the road approached her, Molly was the single one of her kind on the system."

Specifications by Steve Llanso of Sweat House Media
Locobase ID10031
RailroadSaint Louis, Iron Mountain & Southern (MP)
Number in Class1
Road Numbers4000
Number Built1
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase15'
Engine Wheelbase56.58'
Ratio of driving wheelbase to overall engine wheebase 0.27
Overall Wheelbase (engine & tender)85.19'
Axle Loading (Maximum Weight per Axle)
Weight on Drivers395000 lbs
Engine Weight435000 lbs
Tender Light Weight160000 lbs
Total Engine and Tender Weight595000 lbs
Tender Water Capacity8000 gals
Tender Fuel Capacity (oil/coal)14 tons
Minimum weight of rail (calculated)82 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter55"
Boiler Pressure200 psi
High Pressure Cylinders (dia x stroke)26" x 32"
Low Pressure Cylinders (dia x stroke)40" x 32" (2)
Tractive Effort94007 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.20
Heating Ability
Firebox Area252 sq. ft
Grate Area84 sq. ft
Evaporative Heating Surface4533 sq. ft
Superheating Surface890 sq. ft
Combined Heating Surface5423 sq. ft
Evaporative Heating Surface/Cylinder Volume230.52
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation16800
Same as above plus superheater percentage19488
Same as above but substitute firebox area for grate area58464
Power L15437
Power MT242.76


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