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".
|Class||Road Numbers||Year Built||Builder|
|MT-63||5201 - 5207||1913||ALCO|
|MT-73||5308 - 5312||1921||ALCO|
|MT-73||5313 - 5316||1923||ALCO|
|MT-73||5335 - 5339||1927||ALCO|
|MT-73||5340 - 5344||1930||ALCO|
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.
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.
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|
|Class||MT-63||MT-73 - 1921||MT-73 - 1927|
|Railroad||Missouri Pacific (MP)||Missouri Pacific (MP)||Missouri Pacific (MP)|
|Locomotive Length and Weight|
|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 Drivers||208000 lbs||226000 lbs||267500 lbs|
|Engine Weight||296000 lbs||335000 lbs||396000 lbs|
|Tender Light Weight||163000 lbs||192800 lbs||320000 lbs|
|Total Engine and Tender Weight||459000 lbs||527800 lbs||716000 lbs|
|Tender Water Capacity||8000 gals||10000 gals||14000 gals|
|Tender Fuel Capacity (oil/coal)||4250 gals||16 tons||18 tons|
|Minimum weight of rail (calculated) on which locomotive could run||87 lb/yard||94 lb/yard||111 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||170 psi||210 psi||250 psi|
|Cylinders (dia x stroke)||28" x 28"||27" x 30"||27" x 30"|
|Tractive Effort||50350 lbs||53477 lbs||63663 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.13||4.23||4.20|
|Firebox Area||255 sq. ft||327 sq. ft||451 sq. ft|
|Grate Area||56.30 sq. ft||67 sq. ft||84.30 sq. ft|
|Evaporative Heating Surface||3455 sq. ft||3934 sq. ft||5092 sq. ft|
|Superheating Surface||785 sq. ft||1084 sq. ft||1352 sq. ft|
|Combined Heating Surface||4240 sq. ft||5018 sq. ft||6444 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||173.14||197.88||256.13|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||9571||14070||21075|
|Same as above plus superheater percentage||11389||17165||25501|
|Same as above but substitute firebox area for grate area||51587||83777||136428|