Nacional de Mexico 4-8-4 Locomotives in Mexico

Class Details by Steve Llanso of Sweat House Media

Class QR-1 (Locobase 974)

Data from NdeM 1946 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

Built by Alco-Schenectady (16 - works numbers 74380-74387, 74825-74832 in 1946; road numbers 3025-3032, 3049-3056) and Baldwin (16 - works numbers 73018-73033, road numbers 3033-3048) for freight service. Drury (1993) notes that they were among the lightest of Northerns. NdeM called them "Niagaras." The last of these was retired in 1965. (A 1947 Alco advertisement in the Locomotive Cyclopedia shows a superheat area of 1,667 sq ft.) Firebox heating surface included 97 sq ft in three thermic syphons. Valve travel measured 8" with a lead of 1/4".

See the Pennsylvania-based New Hope and Ivyland's website ([], last accessed 3 July 2006) for an encomium, which says in part:

"Built in ...1946 by the American Locomotive Company in Schenectady, New York, these nimble and graceful engines were the finest match between a locomotive design and the environment of its railroad that was ever achieved during the steam era.

"Thoroughly modern in appearance and in specifications, these 32 engines brought a welcomed increase to the roster of the hard working N. de M. Their design included a wisely balanced compromise of features that was absolutely essential for the widely diversified areas where they ran ....For over 20 years these "Niagaras" served throughout Mexico, handling heavy international freight and passenger movements between Mexico City and Nuevo Lare[d]o as well as regular runs to Guadalajara and Aguascalientes through the difficult high altitude mountain country"

The NH & I site claims that the multiplication of axles coincident with adopting the 4-8-4 "...gave the N. de M. the broadest possible usage over the limitations of

the light rail and mountain curves making up much of its right of way." Yet, the minimum average axle loading was 60,000 lb (27.22 metric tons) which required a rail weight of at least 100 lb/yard (49.4 kg/m), which does not imply lightly built track.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID974
RailroadNacional de Mexico (NdeM)
Number in Class32
Road Numbers3025-3056
Number Built32
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)18.25 / 5.56
Engine Wheelbase (ft / m)45.09 / 13.74
Ratio of driving wheelbase to overall engine wheebase 0.40
Overall Wheelbase (engine & tender) (ft / m)86.31 / 26.31
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)240,000 / 108,862
Engine Weight (lbs / kg)387,000 / 175,540
Tender Loaded Weight (lbs / kg)242,400 / 109,951
Total Engine and Tender Weight (lbs / kg)629,400 / 285,491
Tender Water Capacity (gals / ML)15,000 / 56.82
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)6000 / 22.70
Minimum weight of rail (calculated) (lb/yd / kg/m)100 / 50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)70 / 1778
Boiler Pressure (psi / kPa)255.30 / 17.60
High Pressure Cylinders (dia x stroke) (in / mm)25" x 30" / 635x762
Tractive Effort (lbs / kg)58,126 / 26365.54
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.13
Heating Ability
Firebox Area (sq ft / m2)437 / 40.61
Grate Area (sq ft / m2)77.30 / 7.18
Evaporative Heating Surface (sq ft / m2)4185 / 388.94
Superheating Surface (sq ft / m2)1721 / 159.94
Combined Heating Surface (sq ft / m2)5906 / 548.88
Evaporative Heating Surface/Cylinder Volume245.54
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation19,735
Same as above plus superheater percentage25,458
Same as above but substitute firebox area for grate area143,920
Power L138,199
Power MT1403.57

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