Western Pacific 2-6-6-2 "Mallet Mogul" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class M-80 (Locobase 3101)

Data from WP All-Time Steam Locomotive Diagrams supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection. See also Guy Dunscomb, Album of Western Locomotives (Modesto, Calif: Guy Dunscomb, 1952), p. 55.

Frank Brehm's roster at [] (accessed 3 July 2006) gives details of the class: Five were built by Brooks in 1917 (works numbers 57444-57448) for $52,861 each and five more came from Richmond in 1924 (works numbers 65485-65489). Wartime inflation had taken its toll, however -- unit price for this quintet was $83,405.

Firebox heating surface originally included 26 sq ft (2.42 sq m) of arch tubes and amounted to 386 sq ft. (35.86 sq m) The later heating surface value shown in the specs included 84 sq ft (7.8 sq m) of thermic syphons in the firebox and combustion chamber. 14" (356 mm) piston valves supplied steam to the HP cylinders; LP cylinders used slide valves.

They originally took on the Feather River Canyon run between Oroville and Portola, Calif. M-137 s, which could take singly trains that required an M-80 and an MK-60 together, replaced the M-80s in 1931. The

Still useful, the class then ran over the Northern California Extension--203 miles (324 km) of railway between Keddie and Bieber, "through the least inhabited and most beautiful parts of California," wrote Guy Dunscombe, until the end of steam.

Principal Dimensions by Steve Llanso of Sweat House Media

Locobase ID3101
RailroadWestern Pacific (WP)
Number in Class10
Road Numbers201-210
Number Built10
BuilderAlco - multiple works
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)20.67 / 6.30
Engine Wheelbase (ft / m)49.83 / 15.19
Ratio of driving wheelbase to overall engine wheelbase 0.41
Overall Wheelbase (engine & tender) (ft / m)86.48 / 26.36
Axle Loading (Maximum Weight per Axle) (lbs / kg)59,250 / 26,875
Weight on Drivers (lbs / kg)356,500 / 161,706
Engine Weight (lbs / kg)429,500 / 194,818
Tender Loaded Weight (lbs / kg)212,660 / 96,461
Total Engine and Tender Weight (lbs / kg)642,160 / 291,279
Tender Water Capacity (gals / ML)12,000 / 45.45
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)4000 / 15,140
Minimum weight of rail (calculated) (lb/yd / kg/m)99 / 49.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)57 / 1448
Boiler Pressure (psi / kPa)200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)23.5" x 32" / 597x813
Low Pressure Cylinders (dia x stroke) (in / mm)37" x 32" / 940x813
Tractive Effort (lbs / kg)75,112 / 34070.27
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.75
Heating Ability
Tubes (number - dia) (in / mm)235 - 2.25" / 57
Flues (number - dia) (in / mm)36 - 5.5" / 140
Flue/Tube length (ft / m)24 / 7.32
Firebox Area (sq ft / m2)444 / 41.25
Grate Area (sq ft / m2)72.20 / 6.71
Evaporative Heating Surface (sq ft / m2)4936 / 458.74
Superheating Surface (sq ft / m2)1051 / 97.68
Combined Heating Surface (sq ft / m2)5987 / 556.42
Evaporative Heating Surface/Cylinder Volume307.21
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation14,440
Same as above plus superheater percentage17,039
Same as above but substitute firebox area for grate area104,784
Power L17927
Power MT294.13

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