Class 6000 (Locobase 152)

Data from tables in 1930 Locomotive Cyclopedia.

Firebox had combustion chamber. One of three 3-cylinder locomotive designs built by Alco in 1925. (The others were Rock Island's P-46 class and L&N's #295.) The MP was the heaviest and had a slightly higher superheat/CHS ratio. It also had by far the biggest tender.

As noted in the entry on MoPac's 3-cylinder 2-8-2 (#22), trials showed low fuel consumption and impressive tractive effort. In service, however, the maintenance demands of that inside third cylinder outweighed any performance benefit. For a long time, 6000 sat idle, then was rebuilt as essentially a new 2-cylinder engine; see Locobase 9394.

Class 6001 (Locobase 9394)

Data from MP7 - 1956 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Locobase 152 shows the original locomotive 6000 as it was delivered in 1925 with its 3-cylinder layout. As noted, the 3-cylinder arrangement's additional power never quite justified the cost. So after letting the orphan sit idle for several years, the MP completely rebuilt it.

Conversion first as a poppet-valves testbed, then with roller bearings, removal of the third cylinder, oil firing, and Elesco feedwater heater. When completed, the new/old engine had 2 27 x 28" cylinders, a boiler pressed to 200 psi and possessing 4,028 sq ft of heating surface, thermic syphons in the firebox..

Although tractive effort remained about the same, the overhaul transformed the now-renumbered 6001 and she proved a powerful and reliable engine until her 1952 retirement. Her only weak spot was the "poor man's feedwater heater," the Elesco ES. This proved a problematical device that was very sensitive to bad water. When on her mettle, however, the 6001 hit 90-95 mph regularly.

Even so, the MP saw no particular need to retrofit any of its other Pacifics in a similar way.

See WM Adams (Trains, November 1978) for a full account of the modified 6001 "Madame Queen" and the prodigies of speed of which she was capable.

Class P-69 (Locobase 151)

Among the first Pacifics, these had the then-common inside valve motion and trailing-truck bearings. Firebox heating surface included 22 sq ft of arch tubes. Data from AERJ July 1903, supplemented by data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Two number sequences, the first for Missouri Pacific, the other for Iron Mountain. The 1905 renumbering put in the 6501-6521 sequence. All were rebuilt with Baker valve gear (except one with Walschaerts) driving outside piston valves and the steam was superheated. The last left service in 1953.

Class P-69 - superheated (Locobase 9396)

Data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Locobase 151 shows these pioneering Pacifics in their original saturated-steam configuration. All were rebuilt with Baker valve gear (except one with Walschaerts) driving outside 11" piston valves and the steam was superheated. In the process, the cylinder diameter grew by an inch and, as usually happened in these early conversions, the boiler lost some of its total evaporative heating surface. Later retrofits added 10 sq ft of arch tubes and 36 sq ft of thermic syphons.

The last left service in 1953.

Class P-73 / 1151 (Locobase 153)

Data from tables in 1930 Locomotive Cyclopedia, supplemented by MP 8 - 1936 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Firebox had combustion chamber. Ran in Texas for the International-Great Northern (1151-1155) and St. Louis, Brownsville & Mexico (1156-1161). The IGNs had Baker gear, Worthington SA feedwater heaters, the others Worthington BLs.

Class P-73 / 6401 (Locobase 9395)

Data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Class P-73 / 6420 (Locobase 1373)

Data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Follow-ons to the Brooks engines, but much bigger. The first 19 were delivered as saturated-steam engines; those are shown in Locobase 9395. By 1912, the class was being delivered with superheaters and the first group was soon converted. In the process, the cylinder volume grew considerably and total evaporative heating surface actually increased. 1921 saw the delivery of 5 more (6440-6444).

In later years, the firebox was modified with 65 sq ft of thermic syphons, which increased the total firebox heating surface to 271 sq ft. The class also received 73" drivers and some had roller bearings and Elesco feedwater heaters.

Class P-73 / 6601 (Locobase 9397)

Data from MP 7 - 1956 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Firebox had combustion chamber. Drury (1993) notes that the first 10 were delivered as 6445-6454; they were renumbered in 1934. The design was an interesting combination of the USRA's Heavy Pacific boiler and the Light Pacific's 73" drivers. Cast trailing trucks were standard. 6614-6619 were oil-burners to provide clean power for the MP's Sunshine Special.

As often happens in such classes, modifications over time ensured variety. By the 1940s, Drury tells us, "...no two engines in the class had the same combination of disk main drivers, roller bearings, pilots, and tender."

The clas was retired in 1949-1954.