The Sacramento General Shops of the Southern Pacific built 49 "Mountains" between 1925 and 1930. These were built in three batches: road numbers 4385 through 4345 designated Class Mt-3 in 1925 and 1926, road numbers 4346 through 4366 designated class Mt-4 built between 1926 and 1929 and road numbers 4367 through 4376 designated Class Mt-5 in 1929 and 1930. These locomotives were essentially copies of the Class Mt-1s. There are no surviving examples of the Southern Pacific "Mountains".
|Class||Road Numbers||Year Built||Builder|
Lone batch among Espee Mountains built for the El Paso & Southwestern (but delivered to the SP) with different running gear.
They were later rebuilt with 28" cylinders and Walschaert valve gear (as in the other batches). Firebox heating surface eventually included 22 sq ft (2.05 sq m) of arch tubes and 94 sq ft (8.75 sq m) in Nicholson thermic syphons. Steam admission came through 14" (356 mm) piston valves.
First batch built by Alco-Schenectady in 1923; later batches in SP shops up through 1929. Each year's batch received a different class ID. 4328-4345 were Mt-3, 4346-4366 were Mt-4, and 4367-4371 were Mt-5.
Another six (Mt-2; see Locobase 1403) were built by and for the El Paso & Southwestern with different running gear;
The Espee Mountains were considered to have been a very successful class. All were delivered with Worthington 4-B feed water heaters mounted on the left side of the boiler. A type C-1 trailing truck booster contributed 10,100 lb to low-speed tractive effort.
They were oil-fired engines that trailed several different kinds of tenders, including some holding 16,152 US gallons (61,135 litres) water, 4,692 gallons (17,759 litres) oil.
Some were later fitted with skyline casings around the boiler and resembled the better-known GS series of express passenger 4-8-4s.
|Principal Dimensions by Steve Llanso of Sweat House Media|
|Railroad||El Paso & Southwestern (SP)||Southern Pacific (SP)|
|Number in Class||6||71|
|Locomotive Length and Weight|
|Driver Wheelbase (ft / m)||19.50 / 5.94||20 / 6.10|
|Engine Wheelbase (ft / m)||43.58 / 13.28||42.25 / 12.88|
|Ratio of driving wheelbase to overall engine wheebase||0.45||0.47|
|Overall Wheelbase (engine & tender) (ft / m)||83.37 / 25.41||83.50 / 25.45|
|Axle Loading (Maximum Weight per Axle) (lbs / kg)||61,800 / 28,032|
|Weight on Drivers (lbs / kg)||262,000 / 118,841||246,000 / 111,584|
|Engine Weight (lbs / kg)||391,000 / 177,355||368,000 / 166,922|
|Tender Loaded Weight (lbs / kg)||257,500 / 116,800||242,400 / 109,951|
|Total Engine and Tender Weight (lbs / kg)||648,500 / 294,155||610,400 / 276,873|
|Tender Water Capacity (gals / ML)||12,300 / 46.59||12,000 / 45.45|
|Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)||20 / 18.20||3790 / 14.40|
|Minimum weight of rail (calculated) (lb/yd / kg/m)||109 / 54.50||103 / 51.50|
|Geometry Relating to Tractive Effort|
|Driver Diameter (in / mm)||73.50 / 1867||73.50 / 1867|
|Boiler Pressure (psi / kPa)||210 / 14.50||210 / 14.50|
|High Pressure Cylinders (dia x stroke) (in / mm)||29" x 30" / 737x762||28" x 30" / 711x762|
|Tractive Effort (lbs / kg)||61,273 / 27793.00||57,120 / 25909.23|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.28||4.31|
|Firebox Area (sq ft / m2)||461 / 42.84||355 / 32.98|
|Grate Area (sq ft / m2)||84.20 / 7.83||75.70 / 7.03|
|Evaporative Heating Surface (sq ft / m2)||5060 / 470.26||4556 / 423.26|
|Superheating Surface (sq ft / m2)||1380 / 128.25||1162 / 107.95|
|Combined Heating Surface (sq ft / m2)||6440 / 598.51||5718 / 531.21|
|Evaporative Heating Surface/Cylinder Volume||220.63||213.09|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||17,682||15,897|
|Same as above plus superheater percentage||21,395||19,076|
|Same as above but substitute firebox area for grate area||117,140||89,460|