Missouri Pacific 4-6-2 "Pacific" Locomotives in the USA

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Class Details by Steve Llanso of Sweat House Media

Class 6000 (Locobase 152)

Data from tables in 1930 Locomotive Cyclopedia. (Thanks to Chris Hohl for the valve gear ID and for pointing out the mixed valve-gear setup, which is described in Alfred Bruce, The Steam Locomotive in America (New York: Bonanza Books, 1952), pp. 201-201, 210.) .)

NB: The direct heating surface (including the firebox heating surface) is an estimate calculated by subtracting the calculated tube heating surface from the reported total evaporative heating surface.

Firebox had combustion chamber. One of three three-cylinder locomotive designs built by Alco in 1925. (The others were Rock Island's P-46 class-Locobase 142-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 three-cylinder 2-8-2 (#22), trials showed low fuel consumption and impressive tractive effort. Bruce's diagram shows that like the other Alco three-cylinder locomotives, all three cylinders were line abreast and roughly equally spaced. But the two right-hand piston valves were closely spaced over the right-hand cylinder and linked together by a solid arm that pivoted around its center, thus actuating first the central valve, then the outside right valve.

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 Rail Data Exchange.

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)

Data from "New Six-Coupled Passenger Locomotive", American Engineer and Railroad Journal, Volume 67, No 8 (August 1902), pp. 236-237. See also MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers for the MP engines were 26614-26618 in June 1902, 28312-28314 in August 1903, and 28410 in April 1904. St Louis, Iron Mountain & Southern locomotives were delivered simultaneously, works numbers 26619-26623 in July 1902 and 28315-28321 in August 1903.

Two number sequences, the first for Missouri Pacific, the other for Iron Mountain. The 1905 renumbering put in the 6501-6521 sequence.

Among the first Pacifics, these had the then-common inside valve motion and trailing-truck bearings. Firebox heating surface included 22 sq ft (2.04 sq m) of arch tubes.

All were rebuilt with Baker valve gear (except one with Walschaerts) driving outside piston valves and the steam was superheated; see Locobase 9396. Tender capacity increased to 7,000 US gallons (26,495 litres) of water and 14 tons (12.7 metric tons) of coal.

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 Rail Data Exchange.

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" (279 mm) 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 (0.93 sq m) of arch tubes and 36 sq ft (3.34 sq m) of thermic syphons.

The last left service in 1953.


Class P-73 (Locobase 14958)

Data from MP 7 - 1956 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (My thanks to Chris Hohl for his 21 February 2013 inquiry that led to several new entries and updates of several more.)

The quintet of express passenger Pacifics bought by the MP in 1921 from Schenectady (Locobase 14957) were continuations of a larger class originally built in 1910-1912. This later batch was fitted with Harter circulating plates (see the earlier entry for full description and bibliographic references).

At a later time, the MP reworked the boiler and firebox considerably. Locobase can't be sure, but he believes that the Harter plates were removed, but the tube count increased by 16. Two thermic syphons replaced the arch tubes in the firebox and contributed 65 sq ft (6 sq m) to direct heating surface. They were fitted with Timken roller bearings, a BK stoker, and power reverse gear.


Class P-73 (Locobase 14957)

Data from "New Locomotives for the Missouri Pacific", Railway Mechanical Engineer, Vol 95, No 10 (October 1921), pp. 609-613; and F G Lister, "Locomotive Boiler Efficiencey by Proper Circulation of Water", The Boiler Maker, Vol 22, No 9 (September 1922), pp. 256-257. (My thanks to Chris Hohl for his 21 February 2013 inquiry that led to several new entries and updates of several more.) Built at Schenectady in April 1921.

Like the other locomotives ordered by the MoPac from Alco in this year, the Pacifics were fitted with Harter Circulating Plates. Locobase 14956 has a full description of this device. (Briefly, a solid plate laid horizontally among the superheater flues and pierced for 2" diameter steam risers sought to encourage circulation from bottom to top.) Arch tubes added 26 sq ft (2.4 sq m) to direct heating surface area and 14" (356 mm) piston valves supplied steam to the cylinders.

These were later rebuilt by the MP with a new boiler; see Locobase 14958.


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 Rail Data Exchange.

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 Rail Data Exchange. (My thanks to Chris Hohl for his 21 February 2013 inquiry that led to several new entries and updates of several more.)

The first half of a large batch of 73" driver Pacifics were delivered with saturated boilers of a relatively small size matched to a modest cylinder volume.


Class P-73 / 6420 (Locobase 1373)

Data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (My thanks to Chris Hohl for his 21 February 2013 inquiry that led to several new entries and updates of several more.)

The 6420-6439 were follow-ons to the Brooks engines, but much bigger and fitted with square cylinders (bore equalled stroke) that increased cylinder volume by a third. 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) fitted with Harter circulating plates (Locobase 14958).

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 Rail Data Exchange.

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.

Specifications by Steve Llanso of Sweat House Media
Class60006001P-69P-69 - superheatedP-73
Locobase ID152 9394 151 9396 14,958
RailroadMissouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)
CountryUSAUSAUSAUSAUSA
Whyte4-6-24-6-24-6-24-6-24-6-2
Number in Class1121215
Road Numbers600060011115-1123, 1616-16271115-1123, 1616-16276440-6444
GaugeStdStdStdStdStd
Number Built121
BuilderAlcoMPAlco-BrooksMPAlco-Schenectady
Year1925194219021916
Valve GearWalschaertpoppetStephensonBakervarious
Locomotive Length and Weight
Driver Wheelbase (ft / m)14.33 / 4.3714.33 / 4.3712.33 / 3.7612.33 / 3.7613 / 3.96
Engine Wheelbase (ft / m)36.58 / 11.1536.58 / 11.1530.42 / 9.2731.67 / 9.6533.58 / 10.24
Ratio of driving wheelbase to overall engine wheebase 0.39 0.39 0.41 0.39 0.39
Overall Wheelbase (engine & tender) (ft / m)76.17 / 23.2276.17 / 23.2255.12 / 16.8055.17 / 16.8267.02 / 20.43
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)191,000 / 86,636187,785 / 85,178120,000 / 54,431124,000 / 56,246176,850 / 80,218
Engine Weight (lbs / kg)311,000 / 141,067314,755 / 119,755173,000 / 78,472193,000 / 87,543282,300 / 128,049
Tender Loaded Weight (lbs / kg)110,000 / 49,895148,400 / 67,313
Total Engine and Tender Weight (lbs / kg)283,000 / 128,367341,400 / 154,856
Tender Water Capacity (gals / ML)12,000 / 45.4518,000 / 68.185000 / 18.947000 / 26.52
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)16 / 14.505650 / 21.4010 / 9.1014 / 12.70
Minimum weight of rail (calculated) (lb/yd / kg/m)106 / 53104 / 5267 / 33.5069 / 34.5098 / 49
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)73 / 185473 / 185469 / 175369 / 175373 / 1854
Boiler Pressure (psi / kPa)190 / 13.10200 / 13.80200.20 / 13.80200 / 13.80200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)22.5" x 28" / 572x711 (3)27" x 28" / 686x71120" x 26" / 508x66021" x 26" / 533x66026" x 26" / 660x660
Tractive Effort (lbs / kg)47,040 / 21337.0147,535 / 21561.5425,649 / 11634.2028,250 / 12814.0040,930 / 18565.56
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.06 3.95 4.68 4.39 4.32
Heating Ability
Firebox Area (sq ft / m2)254 / 23.61264 / 24.54174 / 16.16221 / 20.54271 / 25.18
Grate Area (sq ft / m2)66.70 / 6.2067.20 / 6.2542.40 / 3.9442.40 / 3.9449.50 / 4.60
Evaporative Heating Surface (sq ft / m2)3624 / 336.804028 / 374.352953 / 274.342322 / 215.803511 / 326.18
Superheating Surface (sq ft / m2)1019 / 94.701354 / 125.84430 / 39.96778 / 72.28
Combined Heating Surface (sq ft / m2)4643 / 431.505382 / 500.192953 / 274.342752 / 255.764289 / 398.46
Evaporative Heating Surface/Cylinder Volume187.50217.08312.36222.78219.75
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation12,67313,440848884809900
Same as above plus superheater percentage15,46116,8008488983711,682
Same as above but substitute firebox area for grate area58,87766,00034,83551,27263,956
Power L116,82222,994931016,10218,075
Power MT582.50809.86513.13858.84675.97

Specifications by Steve Llanso of Sweat House Media
ClassP-73P-73 / 1151P-73 / 6401P-73 / 6420P-73 / 6601
Locobase ID14,957 153 9395 1373 9397
RailroadMissouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)
CountryUSAUSAUSAUSAUSA
Whyte4-6-24-6-24-6-24-6-24-6-2
Number in Class510194029
Road Numbers6440-64441151-11616401-64196420-6439 (+ rebuilds)6601-6629
GaugeStdStdStdStdStd
Number Built510192029
BuilderAlco-SchenectadyAlcoAlcoAlcoAlco
Year19211926191019121924
Valve GearvariousBakerWalschaertWalschaertBaker or Walschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)13 / 3.9613 / 3.9613 / 3.9613 / 3.9613 / 3.96
Engine Wheelbase (ft / m)33.58 / 10.2435.25 / 10.7433.25 / 10.1333.25 / 10.1335.25 / 10.74
Ratio of driving wheelbase to overall engine wheebase 0.39 0.37 0.39 0.39 0.37
Overall Wheelbase (engine & tender) (ft / m)67.02 / 20.4374.83 / 22.8165.29 / 19.9065.29 / 19.9074.83 / 22.81
Axle Loading (Maximum Weight per Axle) (lbs / kg)63,800 / 28,939
Weight on Drivers (lbs / kg)166,500 / 75,523190,520 / 86,419156,000 / 70,760160,500 / 72,802197,700 / 89,675
Engine Weight (lbs / kg)267,500 / 121,336294,000 / 133,356246,000 / 111,584256,000 / 116,120312,810 / 141,888
Tender Loaded Weight (lbs / kg)168,200 / 76,294256,400 / 116,301156,500 / 70,987156,500 / 70,987256,400 / 116,301
Total Engine and Tender Weight (lbs / kg)435,700 / 197,630550,400 / 249,657402,500 / 182,571412,500 / 187,107569,210 / 258,189
Tender Water Capacity (gals / ML)8000 / 30.3012,000 / 45.458000 / 30.308000 / 30.3012,000 / 45.45
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)14 / 12.705000 / 18.9014 / 12.7014 / 12.706610 / 25
Minimum weight of rail (calculated) (lb/yd / kg/m)93 / 46.50106 / 5387 / 43.5089 / 44.50110 / 55
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)73 / 185473 / 185469 / 175369 / 175373 / 1854
Boiler Pressure (psi / kPa)190 / 13.10188.50 / 13200 / 13.80180 / 12.40200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)26" x 26" / 660x66027" x 28" / 686x71123" x 25" / 584x63526" x 26" / 660x66027" x 28" / 686x711
Tractive Effort (lbs / kg)38,884 / 17637.5144,802 / 20321.8732,583 / 14779.4238,973 / 17677.8847,535 / 21561.54
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.28 4.25 4.79 4.12 4.16
Heating Ability
Firebox Area (sq ft / m2)233 / 21.65266 / 24.72209.70 / 19.49209.70 / 19.49274 / 25.46
Grate Area (sq ft / m2)49.50 / 4.6067.80 / 6.3050 / 4.6549.50 / 4.6067.80 / 6.30
Evaporative Heating Surface (sq ft / m2)3283 / 3053719 / 345.634108 / 381.783450 / 320.633904 / 362.83
Superheating Surface (sq ft / m2)778 / 72.281054 / 97.96722 / 67.10980 / 91.08
Combined Heating Surface (sq ft / m2)4061 / 377.284773 / 443.594108 / 381.784172 / 387.734884 / 453.91
Evaporative Heating Surface/Cylinder Volume205.48200.43341.71215.93210.40
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation940512,78010,000891013,560
Same as above plus superheater percentage11,19215,59210,00010,42516,272
Same as above but substitute firebox area for grate area52,68161,17241,94044,16365,760
Power L116,56717,965986514,24718,483
Power MT658.09623.65418.24587.09618.33

Reference