These classic engines were based to a large extent on the Western Pacific's M-137-151 2-8-8-2 engines of 1931 (Locobase 332), but were lengthened to take an all-weather cab . The DM & IR engines burned bituminous coal and had a smaller grate area than the oil-burning M-137s although the overall firebox heating surface grew by 11 sq ft (1 sq m). In the M-4, this total included 194 sq ft (18 sq m) in three thermic syphons, 177 sq ft (16.45 sq m) in the combustion chamber, and 32 sq ft (3 sq m) of arch tubes. As part of the M-137 revision, the combustion chamber's length grew from 6 to 7 feet (2,134 mm).
Boiler tube and flue length (sheet to sheet) was shortened by 2 feet to 21 feet (6.4 m). The mixture of tubes and flues changed as the design substituted a Type E superheater for the M-137's Type A. The number of 2 1/4-in flues decreased to 82 and Baldwin installed 245 of the 3 3/4-in flues (vs. the M-137's 270 of the former and 75 5 1/2-in flues) . As a result, superheater area increased by 25%. The first five M-4s had Worthington feedwater heaters, the last five Elescos. Four piston valves each measured 12" (306 mm) in diameter.
Following contemporary practice, the M-3s had integrally cast frames and cylinders, Timken roller bearings on all driving axles, ASF (M-3) or SKF (M-4) roller bearings on all truck axles.
These engines performed very well from the time they entered service in May 1941, soon handling train loads 25% heavier than the earlier M-1/M-2 engines could manage. The last ten engines were M-4s, built by Baldwin in 1943, which used carbon steel in certain components because of a shortage of high-tech alloy steels. They had an engine weight of 699,700 lb (317,379 kg).
During 1943-44, as many as 12 "Yellowstones" were operating on the D & RGW, the GN, and the NP under lease where they were highly regarded. In fact, the D & RGW telegraphed the DM&IR with the claim that these Yellowstones were the finest engines ever to run on the Rio Grande.
The Lake Superior Railroad Museum site -- http://www.lsrm.org/Museum/mallet.htm (visited 9 Feb 2004) -- gives some interesting consumption numbers: " When working at full power, [the locomotive] could consume some 10 to 12 tons of coal an hour and evaporate water into steam at the astounding rate of 12,000 gallons per hour. The amount of coal ...used in one hour would be enough to heat a home for two winters." (and Minnesota winters at that, one supposes.)
|Specifications by Steve Llanso of Sweat House Media|
|Railroad||Duluth, Missabe & Iron Range (DM&IR)|
|Number in Class||18|
|Locomotive Length and Weight|
|Ratio of driving wheelbase to overall engine wheebase||0.26|
|Overall Wheelbase (engine & tender)||113.49'|
|Axle Loading (Maximum Weight per Axle)|
|Weight on Drivers||560257 lbs|
|Engine Weight||695040 lbs|
|Tender Light Weight||438000 lbs|
|Total Engine and Tender Weight||1133040 lbs|
|Tender Water Capacity||25000 gals|
|Tender Fuel Capacity (oil/coal)||26 tons|
|Minimum weight of rail (calculated)||117 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||240 psi|
|Cylinders (dia x stroke)||26" x 32"|
|Tractive Effort||140093 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.00|
|Firebox Area||750 sq. ft|
|Grate Area||125 sq. ft|
|Evaporative Heating Surface||6782 sq. ft|
|Superheating Surface||2770 sq. ft|
|Combined Heating Surface||9552 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||172.45|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||30000|
|Same as above plus superheater percentage||38700|
|Same as above but substitute firebox area for grate area||232200|