Denver & Rio Grande 2-4-0 "Porter" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class Montezuma/Class 25 (Locobase 1448)

Data from "Narrow gauge (3 feet) Passenger Locomotive, by the Baldwin Locomotive Works, for the Denver & Rio Grande Railway", Railroad Gazette, Volume 3, (5 August 1871), p. 215; [] and from Data from Baldwin Locomotive Works Specification for Engines, as digitized by the DeGolyer Library of Southern Methodist University, Volume 5, p. 217. Works numbers 2459 in May 1871 and 2566 in September.

Early narrow-gauge wood-burners in Colorado. The Baldwin specs add:"Steam Jets in front of Cylinder to scare cattle!" (Exclamation point in the original.) The passenger engines pulled as many as six cars. The latter were supplied by the well-known car builder Jackson & Sharp of Wilmington, Del, then the only such manufacturer for narrow-gauge railroads in the country. (The order was shipped to Denver in July 1871 and arrived 18 days later on 2 August.)

The RG report focused on the flexibility of the locomotive despite its relatively long wheelbase for two axle on the 3 foot gauge. The pony wheels were mounted on a swing bolster that, in conjunction with a radius bar, allowed them to move laterally under the Montezuma. The pony truck was also equalized with the lead driving axle.

RG assessed skepticism about this design's maximum speed potential by pointing out that over a mile, the piston would travel the same distance as a regular engine with a 24" stroke turning 60" drivers. And in truth the Montezuma's driver aspect ratio (diameter/gauge) was the same. But Locobase compared the number of strokes the smaller engine would need to cover a mile (504) compared to the standard-gauge locomotive (336) and figures that at the same speed, the 3-footer would work 50% harder.

Paul T. Warner, Baldwin historian, wrote in a history of the works reproduced in Westing (1966), that this design (works number 2459) was "found to be too small and to be unsteady on the track, owing to its comparatively short wheelbase. It [the type] was therefore abandoned, and the ordinary American pattern, eight-wheeled, four-coupled, substituted." (The layout would endure as suitable for a small sugar-plantation locomotive.)

Cortez joined the Montezuma later in the year. Montezuma was leased to the Denver, Utah and Pacific Railroad, then returned to the Rio Grande in 1883. It was retired in 1887 with Cortez and both were scrapped in July 1888.

Principal Dimensions by Steve Llanso of Sweat House Media
ClassMontezuma/Class 25
Locobase ID1448
RailroadDenver & Rio Grande (D&RGW)
Number in Class2
Road Numbers1, 4
Number Built2
BuilderM. Baird & Co
Valve GearStephenson
Locomotive Length and Weight
Driver Wheelbase (ft / m) 6.25
Engine Wheelbase (ft / m)11.96
Ratio of driving wheelbase to overall engine wheebase 0.52
Overall Wheelbase (engine & tender) (ft / m)36.43
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)20,500
Engine Weight (lbs / kg)25,300 / 11,340
Tender Loaded Weight (lbs / kg)
Total Engine and Tender Weight (lbs / kg)
Tender Water Capacity (gals / ML)500
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT) 1.50
Minimum weight of rail (calculated) (lb/yd / kg/m)17 / 8.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)40 / 1016
Boiler Pressure (psi / kPa)130 / 9
High Pressure Cylinders (dia x stroke) (in / mm)9" x 16" / 229x406
Tractive Effort (lbs / kg)3580 / 1623.86
Factor of Adhesion (Weight on Drivers/Tractive Effort) 5.73
Heating Ability
Firebox Area (sq ft / m2)
Grate Area (sq ft / m2) 6.25 / 0.58
Evaporative Heating Surface (sq ft / m2)
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)
Evaporative Heating Surface/Cylinder Volume
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation813
Same as above plus superheater percentage813
Same as above but substitute firebox area for grate area
Power L1
Power MT

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