Missouri Pacific 4-8-2 "Mountain" Type Locomotives

Introduction

The Missouri Pacific took delivery of seven 4-8-2s from the American Locomotive Company in 1913. These locomotives, designated Class MT-63, were relatively light (296,000 lbs), and were assigned road numbers 5201 through 5207. They had 63" diameter drivers and exerted 51,075 lbs of tractive effort. The seven "Mountains" were put to work on the St. Louis, Iron Mountain & Southern for the St. Louis - Little Rock passenger traffic.

In 1919, the USRA supplied seven more "Light Mountains" with 69" drivers. They were buit by ALCO and were designated,class MT-69 and assigned road numbers 5301 through 5307.

Between 1921 and 1930 the MoPac took delivery of nineteen class MT-73 "Mountains" from ALCO. These locomotives arrived in four batches: road numbers 5308 through 5312 came in 1921, road numbers 5313 through 5316 in 1923, road numbers 5335 through 5339 in 1927 and the final batch, road numbers 5340 through 5344 arrived in 1930. The last five class MT-73s had 27 x 30 cylinders, 73" drivers, a 250 psi boiler pressure and exerted 63,662 lbs of tractive effort.

In 1939, the Sedalia Shops rebuilt the seven Class MT-69 locomotives that were delivered in 1919. These rebuilt locomotives were given 75" drivers, new boilers, lightweight rods, roller bearings and new tenders. With the new boilers the steam pressure was raised to 250 psi. They were also converted to burn oil and were assigned new road numbers (5321 through 5327) and designated Class MT-75.

There are no surviving Missouri Pacific "Mountains".

Roster by Richard Duley

ClassRoad NumbersYear BuiltBuilder
MT-635201 - 52071913ALCO
MT-695301 -53071919ALCO
MT-735308 - 53121921ALCO
MT-735313 - 53161923ALCO
MT-735335 - 53391927ALCO
MT-735340 - 53441930ALCO
Note: The seven Class MT-69 locomotives, road numbers 5301 - 5307, were rebuilt in 1939 and were designated Class MT-75 and given new road numbers 5321 through 5327.

Class Details by Steve Llanso

Class MT-63 (Locobase 10049)

Data from 1924 MP locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive collection.

There were not at all like the definitive Mountains that would enter service on many roads just a few years later. Indeed, they were more like Mikados with a leading bogie than a true 4-8-2. Still, they must have served a useful purpose because the firebox would later be enhanced with 65 sq ft of thermic syphons and they would remain in service until 1948.

Class MT-73 - 1921 (Locobase 14956)

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 by Schenectady in 1921 (5308-5312) and 1923 (5313-5316).

According to the RME report, the MoPac faced contradictory requirements for its heavy passenger engines not long after World War One. Demands for greater capacity and speed meant the MT-63s built in the 'teens simply weren't big enough. At the same time, bridges and other structures forced the railroad to hold adhesive weight in any new design to 113 short tons.

Believing that more efficient use of boiler surface allowed for a smaller boiler, Charles Harter, an MP mechanical engineer devised curved circulating plates, which were estimated to add 10% to the boiler's capacity. At a point just behind the feedwater inlet and slightly below the boiler centerline, the horizontal plate spanned the width of the boiler and extended back to within 4-5" (102-127 mm) of the back tube sheet and 30" (762 mm) of the front sheet. Two-inch (50.8-mm) diameter steam risers were inserted at intervals in the sheet so that they stood vertically among the upper three ranks of 5 1/2" flues and allowed steam generated below the plate to join steam in the upper boiler.

RME reported that the boilers steamed "just as freely as the older ones, are running with 3/4" larger exhaust nozzles, are making better fuel records, and take the same train 30 miles (48.3 km) further for water." Lister quoted Harter as claiming that the boiler raised steam to the desired pressure in 30-45 minutes less time.

In addition to the circulating plates, these engines benefited from a high degree of superheat, 27 sq ft (2.5 sq m) of arch tubes, and 14" (356 mm) piston valves

In later years, the MP rebuilt at least some of the class with new boilers containing 199 tubes and a revamped firebox that had two arch tubes and two thermic syphons. The two additions contributed 13 and 62 sq ft (1.2 and 5.75 sq m) respectively to a total direct heating surface area of 312 sq ft (29 sq m). The design now included an Elesco feed water heater.

See Locobase 211 for the larger and more conventional MT-73s supplied later in the decade.

Class MT-73 - 1927 (Locobase 211)

Data from tables in 1930 Locomotive Cyclopedia. See also MP 7 - 1956 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. (Thanks to Chris Hohl for spotting the error in the valve gear field and for his 21 February 2013 inquiry that led to several new entries and updates of several more.) Built by Brooks (5335-5339) and Schenectady (5340-5344)

Apparently, the MT-73s produced by Schenectady in 1921 and 1923 (Locobase 14956) were still too small for the ever-burgeoning heavy passenger traffic. So they ordered much larger locomotives from Brooks and Schenectady and operated them on routes that featured a beefed-up right of way.

In their final form (shown here), these engines had a generous amount of both superheat and firebox heating surface area. The latter included 18 sq ft (1.7 sq m) in arch tubes and 76 sq ft (7.05 sq m) of thermic syphons. (5337's firebox used Martin circulators totalling 59 sq ft/ 5.5 sq m.)

All of these engines had power reverse gear, BK stokers, Worthington 4 1/4 BL 2 feed water heaters, cast steel locomotive beds, and roller bearings.


Specifications by Steve Llanso
ClassMT-63MT-73 - 1921MT-73 - 1927
Locobase ID10049 14956 211
RailroadMissouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)
Whyte4-8-24-8-24-8-2
Road Numbers5201-52075308-53165335-5344
GaugeStdStdStd
BuilderAlcoAlco-SchenectadyAlco
Year191319211927
Valve GearBakerWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase16.50'19.58'19.58'
Engine Wheelbase36.83'41.33'42.17'
Ratio of driving wheelbase to overall engine wheebase 0.45 0.47 0.46
Overall Wheelbase (engine & tender)70.52'77.17'88.37'
Axle Loading (Maximum Weight per Axle)
Weight on Drivers208000 lbs226000 lbs267500 lbs
Engine Weight296000 lbs335000 lbs396000 lbs
Tender Light Weight163000 lbs192800 lbs320000 lbs
Total Engine and Tender Weight459000 lbs527800 lbs716000 lbs
Tender Water Capacity8000 gals10000 gals14000 gals
Tender Fuel Capacity (oil/coal)4250 gals16 tons18 tons
Minimum weight of rail (calculated) on which locomotive could run87 lb/yard94 lb/yard111 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter63"73"73"
Boiler Pressure170 psi210 psi250 psi
Cylinders (dia x stroke)28" x 28"27" x 30"27" x 30"
Tractive Effort50350 lbs53477 lbs63663 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.13 4.23 4.20
Heating Ability
Firebox Area255 sq. ft327 sq. ft451 sq. ft
Grate Area56.30 sq. ft67 sq. ft84.30 sq. ft
Evaporative Heating Surface3455 sq. ft3934 sq. ft5092 sq. ft
Superheating Surface785 sq. ft1084 sq. ft1352 sq. ft
Combined Heating Surface4240 sq. ft5018 sq. ft6444 sq. ft
Evaporative Heating Surface/Cylinder Volume173.14197.88256.13
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation95711407021075
Same as above plus superheater percentage113891716525501
Same as above but substitute firebox area for grate area5158783777136428
Power L1105511969529858
Power MT447.33768.50984.31

Photos

Reference

Credits

Introduction and roster provided by Richard Duley. Class details and specifications provided by Steve Llanso of Sweat House Media.