Drury (1993) comments that this trio were light and low-drivered machines, "...but low drivers were what the 4.7% grade called for." Locobase guesses that the engines were superheated after delivery, possibly when the fireboxes also gained 52 sq ft of Nicholson thermic syphons.
It was somewhat unusual for a North American railroad to persevere with the 3-cylinder layout more than a few years after its introduction. The Mexican Railway broke that mold in two ways: it ordered 3 more MR-3s 10 years after the first 4 had come on the road, and those locomotives remained in service as 3-cylinder engines into the 1960s.
The 1928 quartet came from Schenectady (works 67557-67560). Montreal Locomotive Works supplied the other three (Alco works #69061-69063); these weighed about a short ton more. All had their firebox heating surface supplemented by 13 sq ft of arch tubes and 63 sq ft (in the 1928 locomotives) or 59 sq ft (1938) of Nicholson thermic syphons.
Unfortunately, the diagrams do not show superheater area; that number comes from Dr Jonathan Smith's Standard Steam Locomotive tables http://orion.math.iastate.edu/jdhsmith/term/slmxfnm.htm .
| Specifications | ||
|---|---|---|
| Class | M | MR-3 |
| Locobase ID | 6743 | 6744 |
| Railroad | Mexican Railway | Mexican Railway |
| Whyte | 4-6-2 | 4-6-2 |
| Road Numbers | 120-122 | 130-133, 134-136 |
| Gauge | Std | Std |
| Builder | Baldwin | several |
| Year | 1910 | 1928 |
| Valve Gear | Baker | Baker |
| Locomotive Length and Weight | ||
| Driver Wheelbase | 11.83' | 13.83' |
| Engine Wheelbase | 31.33' | 34.50' |
| Ratio of driving wheelbase to overall engine wheebase | 0.38 | 0.40 |
| Overall Wheelbase (engine & tender) | 60.58' | 63.92' |
| Axle Loading (Maximum Weight per Axle) | ||
| Weight on Drivers | 138536 lbs | 147998 lbs |
| Engine Weight | 219424 lbs | 249997 lbs |
| Tender Light Weight | 120000 lbs | 129800 lbs |
| Total Engine and Tender Weight | 339424 lbs | 379797 lbs |
| Tender Water Capacity | 6000 gals | 6000 gals |
| Tender Fuel Capacity (oil/coal) | 2500 gals | 2500 gals |
| Minimum weight per yard of rail on which locomotive could run | 76.96 lb rail | 82.22 lb rail |
| Geometry Relating to Tractive Effort | ||
| Driver Diameter | 63" | 69" |
| Boiler Pressure | 180 psi | 200 psi |
| Cylinders (dia x stroke) | 23" x 28" | 20" x 28" (3) |
| Tractive Effort | 35972 lbs | 41391 lbs |
| Factor of Adhesion (Weight on Drivers/Tractive Effort) | 3.85 | 3.58 |
| Heating Ability | ||
| Firebox Area | 234 sq. ft | 259 sq. ft |
| Grate Area | 47.50 sq. ft | 52 sq. ft |
| Evaporative Heating Surface | 1987 | 2823 |
| Superheating Surface | 490 | 760 |
| Combined Heating Surface | 2477 | 3583 |
| Evaporative Heating Surface/Cylinder Volume | 147.57 | 184.85 |
| Computations Relating to Power Output (More Information) | ||
| Robert LeMassena's Power Computation | 8550 | 10400 |
| Same as above plus superheater percentage | 10241.36 | 12605.97 |
| Same as above but substitute firebox area for grate area | 50452.18 | 62787.44 |
| Power L1 | 10621.74 | 16503.41 |
| Power MT | 507.09 | 737.52 |
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