Nacional de Mexico 2-6-6-2 Type Locomotives

Class HR-01 (Locobase 4430)

Data from narrowmind.railfan.net, which reproduces an older "Fig. 3333". Confusing discrepancies between the illustration of this simple-expansion Prairie Mallet here and in Drury (1993). The "figure" shows an engine numbered 242 and laid out roughly the same as the 367 shown in Drury. 242 has its bell located between the steam dome (which is over the two leading drivers of the rear set) and the forward sand dome. Another illustration from narrowmind, this from Durrant's The Mallet Locomotive, shows a similar locomotive with the same data but numbered 369.

Drury's 367 shows the bell positioned over the smokebox, just in front of the Elesco feedwater heater. Its place on the boiler has been taken by another sand dome. Drury doesn't say, but it seems clear that the class was renumbered and otherwise altered after the delivery of the first batch of 6 in 1928. (Two more arrived in 1934 and the final two in 1936.)

In any event, NdeM got for their money a nice balance of power and speed on a narrow gauge.

Class HR-4 (Locobase 3167)

Giving the impression of "being a slightly under-scale Challenger" [4-6-6-4], these standard-gauge freight engines were modern in every respect. Very few Prairie Mallets were built as simple-expansion locomotives, Drury (1993) adds, and the NdeM stud was the largest single class. They served until 1963.

Specifications
Class	HR-01	HR-4
Locobase ID	4430	3167
Railroad	Nacional de Mexico	Nacional de Mexico
Whyte	2-6-6-2	2-6-6-2
Road Numbers	361-370	2030-2037
Gauge	3'	Std
Builder	Alco	Alco
Year	1928	1937
Valve Gear	Walschaert	Walschaert
	Locomotive Length and Weight
Driver Wheelbase
Engine Wheelbase
Ratio of driving wheelbase to overall engine wheebase
Overall Wheelbase (engine & tender)
Axle Loading (Maximum Weight per Axle)	28672 lbs
Weight on Drivers	161500 lbs	322560 lbs
Engine Weight	204000 lbs	400960 lbs
Tender Light Weight
Total Engine and Tender Weight	204000 lbs	400960 lbs
Tender Water Capacity
Tender Fuel Capacity (oil/coal)
Minimum weight per yard of rail on which locomotive could run	44.86 lb rail	89.60 lb rail
	Geometry Relating to Tractive Effort
Driver Diameter	43"	57"
Boiler Pressure	210 psi	250 psi
Cylinders (dia x stroke)	15" x 22" (4)	18" x 30" (4)
Tractive Effort	41097 lbs	72474 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort)	3.93	4.45
	Heating Ability
Firebox Area	204 sq. ft
Grate Area	52.50 sq. ft	70.30 sq. ft
Evaporative Heating Surface	2449	3801
Superheating Surface	680	1080
Combined Heating Surface	3129	4881
Evaporative Heating Surface/Cylinder Volume	272.13	215.09
	Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation	11025	17575
Same as above plus superheater percentage	13420.97	21463.75
Same as above but substitute firebox area for grate area	52150.07	0
Power L1	16036.09	0
Power MT	1313.44	0