All 70 compound Mallets built to the same wheel arrangement were obviously very satisfactory pusher locomotives for the Union Pacific. In 1937, the railroad decided to modify the cylinder layout to all live steam. It's a bit unusual for the rebuild to shorten the stroke on the drivers, which the UP did in this program. Tractive effort is listed as 89,840 lb on the diagram, which shows no grate area because these were oil burners. 46 sq ft of the firebox heating surface came in the form of arch tubes.
The 70 locomotives were converted in 1937-1943. Some of the conversions operated until 1954.
This low-drivered design was the first of a series of pusher freight compounds.
In addition to the Union Pacific's 15, the Oregon Short Lines took 1 engine of the Schenectady batch of MC-2s. These were followed in 1920 by 19 Brooks-built engines of similar dimensions and greater weight; like the MC-2s, these had 15" piston valves on all four cylinders Brooks added 5 more MC-4s in 1922 along identical lines; Oregon Shoort Lines took delivery of 2 in 1923 and the OWR&N took 3. In 1923, Brooks added another 5 as MC-5s.
MC-2 15 from Alco-Schenectady in 1918 3600-3614
MC-3 19 from Alco-Brooks in 1920 3615-3633
MC-4 5 from Alco-Brooks in 1920 3634-3638
MC-5 5 from Alco-Brooks in 1923 3639-3643
MC-6 see above
OSL received 1 MC-2 and 2 MC-4s, OWR&N took 3 MC-4s.
| Specifications | |||
|---|---|---|---|
| Class | MC series - simpled | MC-2/MC-3/MC-4/MC-5 | MC-6 |
| Locobase ID | 7467 | 7466 | 310 |
| Railroad | Union Pacific (UP) | Union Pacific (UP) | Union Pacific (UP) |
| Whyte | 2-8-8-0 | 2-8-8-0 | 2-8-8-0 |
| Road Numbers | 3500-3569 | 3600-3643 | 3645-3664 |
| Gauge | Std | Std | Std |
| Builder | shops | Alco-Schenectady | Alco-Brooks |
| Year | 1937 | 1918 | 1924 |
| Valve Gear | Walschaert | Walschaert | |
| Locomotive Length and Weight | |||
| Driver Wheelbase | 15.50' | 15.50' | 15.50' |
| Engine Wheelbase | 50.50' | 50.50' | 50.50' |
| Ratio of driving wheelbase to overall engine wheebase | 0.31 | 0.31 | 0.31 |
| Overall Wheelbase (engine & tender) | 87.89' | 87.04' | 87.04' |
| Axle Loading (Maximum Weight per Axle) | 57870 lbs | ||
| Weight on Drivers | 447023 lbs | 464730 lbs | 465000 lbs |
| Engine Weight | 501480 lbs | 495500 lbs | 495500 lbs |
| Tender Light Weight | 227280 lbs | 219000 lbs | 219000 lbs |
| Total Engine and Tender Weight | 728760 lbs | 714500 lbs | 714500 lbs |
| Tender Water Capacity | 12000 gals | 12000 gals | 12000 gals |
| Tender Fuel Capacity (oil/coal) | 5200 gals | 20 tons | 20 tons |
| Minimum weight per yard of rail on which locomotive could run | 93.13 lb rail | 96.82 lb rail | 96.88 lb rail |
| Geometry Relating to Tractive Effort | |||
| Driver Diameter | 57" | 57" | 57" |
| Boiler Pressure | 218 psi | 210 psi | 210 psi |
| Cylinders (dia x stroke) | 23" x 30" (4) | 26" x 32" | 26" x 32" |
| Low Pressure Cylinders (dia x stroke) | " x " | 41" x 32" | 41" x 32" |
| Tractive Effort | 103183 lbs | 96627 lbs | 96627 lbs |
| Factor of Adhesion (Weight on Drivers/Tractive Effort) | 4.33 | 4.81 | 4.81 |
| Heating Ability | |||
| Firebox Area | 383 sq. ft | 383 sq. ft | 403 sq. ft |
| Grate Area | 88.20 sq. ft | 88.20 sq. ft | 88.10 sq. ft |
| Evaporative Heating Surface | 5622 | 5668 | 5412 |
| Superheating Surface | 1320 | 1320 | 1397 |
| Combined Heating Surface | 6942 | 6988 | 6809 |
| Evaporative Heating Surface/Cylinder Volume | 194.85 | 288.24 | 275.22 |
| Computations Relating to Power Output (More Information) | |||
| Robert LeMassena's Power Computation | 19227.60 | 18522 | 18501 |
| Same as above plus superheater percentage | 22883.67 | 22020.72 | 22296.84 |
| Same as above but substitute firebox area for grate area | 99370.13 | 95622.84 | 101993.51 |
| Power L1 | 13937.32 | 7940.70 | 8159.79 |
| Power MT | 549.89 | 301.36 | 309.49 |
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