4-6-2 Steam Locomotives in Mexico

Class M-1 (Locobase 5343)

Data from American Engineering and Railroad Journal, February 1907 and "Pacific Type Locomotives - National Railway of Mexico", Railway Master Mechanic, February 1907, pp. 50-52. Works numbers were 41284-41286 in October 1906.

This trio were the most normal of the Pacifics delivered to the NdeM during this period.. For its time, this was a rather big 4-6-2 with a boiler that, as the AERJ article noted, "with a moderately good grade of coal there should be no difficulty in furnishing the all the steam needed." No doubt.

The trio was later superheated; see Locobase 9398.

Class M-2 (Locobase 5344)

Data from "Pacific Type Locomotives - National Railway of Mexico", American Engineer and Railroad Journal, Volume 81, No. 2 (February 1907), p. 70 and "Pacific Type Locomotives - National Railway of Mexico", Railway Master Mechanic, February 1907, pp. 50-52. See also "New Types of Valves and Valve Gears for Locomotives", Engineering News, Vol LIII, No 18 (4 May 1905), p. 458-461.

This engine was identical to the three M-1s (Locobase 5343) delivered at the same time from the same builder except for the valves and cylinders and the provision of cylindrical Vanderbilt tenders. Although the same diameter and stroke, the Alfree-Hubbell valves offered a "delayed opening and closure for all points of cut-off, an increased exhaust area, and a large reduction in cylinder clearance." (The reader is then directed to AERJ September 1906, 334-337, and indeed there is a long article on the design.). The effect was attained through an auxiliary, 5" (127 mm) piston valve with "wide special rings which fit openings in the wall between the steam port and exhaust passages"

AERJ noted that the system had been in service for over a year with "most satisfactory results both as regards economy of operation and maintenance, as well as in giving a very quick and responsive engine."

JB Alfree invented the valve and Ira C Hubbell, then president of the Lunkenheimer Company, was instrumental in adapting the valve to locomotive use. By 1904, the valves were produced by the Locomotive Appliance Company reported to its stockholders that six railroads were operating locomotives with their valves. One was the Pere Marquette, which had three engines with Alfree Hubbell valves. Locobase is not certain how widespread this installation might have been (see Locobase 8979 for a Mogul built for the Denver, Enid & Gulf), but it must not have been very common.

Nor is it likely to have remained on the M-2 for very long. The M-2 was later superheated -- see Locobase 9398 -- and carried on 'til 1956.

Class M-3 (Locobase 5346)

Data from DeGolyer, Volume 30, p. 137; and "Pacific Type Locomotives - National Railway of Mexico", American Engineer and Railroad Journal, Volume 81, No. 2 (February 1907), p. 70. Works number was 29275 in October 1906

It was a Baldwin balanced compound Pacific with an extended wagon-top boiler. Steam was admitted through 15" (381 mm) piston valves. Its tender was a cylindrical Vanderbilt type.

Like Alco's M-4 Cole balanced compound (Locobase 5345), the M-3 soon was converted to a two-cylinder simple-expansion locomotive. Still later it was superheated; see Locobase 9399.

Class M-4 (Locobase 5345)

Data from "Pacific Type Locomotives - National Railway of Mexico", American Engineer and Railroad Journal, Volume 81, No. 2 (February 1907), p. 70.

This engine, delivered at the same time to the three M-1s (Locobas 5343), were identical in boiler and most other dimensions.

Instead of the simple-expansion layout of the M-1 (Locobase 5343), however, the M-4 was a Cole balanced compound similar (virtually identical, in fact) to the Q-2s delivered to the Northern Pacific in the same year. Like the NP engines, this engine had inside admission for the high-pressure piston valves, outside for the low-pressure ones. Note that, unlike most compounds, stroke lengths of this Pacific's LP cylinders were 1" longer than the HP strokes. (The M-4 had a cylindrical Vanderbilt tender.)

Later converted to a two-cylinder simple design, this engine carried on until 1957.

Class MR-1/MR-2/MR-4 (Locobase 9398)

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

Locobases 5343, 5344, and 5345 show the M-1, M-2, and M-4 in their various saturated-boiler states. Sometime later the NdeM superheated all three classes to the same specification and redesignated them MR-1/MR-2 (R=recalentador or superheater). The 1946 book does not give an area for the superheater, so Locobase has made an estimate based on a very similar upgrade to the C & North Western E class.

MR-2's big difference was an adhesion weight of 150,795 lb, while the MR-4 bulked up to 161,000 lb and had a firebox heating surface of 200 sq ft vs the 169 sq ft shown in the specs.

In any case, these engines soldiered on until the mid-1950s.

Class MR-3 - superheated (Locobase 9399)

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

As delivered by Baldwin (Locobase 5346), this locomotive was a Baldwin balanced compound. Later the locomotive was simpled and still later superheated (hence the R in MR-3, which stands for "recalentador"). The superheater area is a Locobase estimate as the 1946 diagram does not provide a separate figure.

Class MR-6 (Locobase 1380)

Railway Age (12 Nov 1921). See also DeGolyer Library, Vol 65, pp. 396+. Works numbers were 54899-54902, 54921-54922 in July 1921; 54944-54947 in August; 55034, 55062-55070 in September; and 57911-57914 in July 1924.

Drury (1993) notes that the KR-1 Mikados, these MR-6s, and the PR-7 4-8-0s all had the same boiler (tubes, grate area, firebox identical). Of the first twenty of these oil-burning Pacifics delivered by Baldwin, ten had Young gear, ten had Baker valve gear; the last four, delivered three years later, had Young gear as well. All had Ragonnet power reverse and 14" (356 mm) piston valves.

The last was retired in 1962.

Class MR-7 (Locobase 9489)

Data from MexRy 1939 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 67703-67704 in October 1928.

Delivered in the same year as the Mexican Railway's three-cylinder engines (see Locobase 6744), these were carbon copies. Identical details included firebox heating surface area supplemented by 13 sq ft (1.21 sq m) of arch tubes and 63 sq ft (5.85 sq m) and Elesco feed water heaters. The only differences were drivers measuring 2" (50.8 mm) smaller in diameter and larger tenders. Although they were Pacifics, the locomotives apparently served the NdeM in many capacities. They were rated to pull 2,300 tons in 57 cars on the level at 25 km/h (15 1/5 mph); at the other end of the spectrum, they were credited with the same speed hauling four cars in a train of 160 tons up a 4% grade.