Norfolk & Western 4-8-0 "Mastodon" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class M (Locobase 2500)

Data taken from Railroad Age Gazette (19 June 1908), supplemented and amended by N&W 3-1955 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

The first of the N&W's "Mollies" (as the crews called these 4-8-0s), these engines were supplied by Alco-Richmond (75) and Baldwin (50). In a long, and very good essay on the N&W "Remarkable 4-8-0s", Thomas Dressler (on notes that these engines were the railroad's main-line freight haulers and very successful this first batch were. Described as a Consolidation with a 4-ft longer boiler, these engines didn't break any new ground but did provide better riding qualities and more power on essentially the same wheelbase.

Other features in these engines were the two arch tubes (which contributed 19 sq ft to the firebox heating surface area) and high-grade refractory brick, 12" piston valves, main rod on the second driving axle, no deck behind the firebox (soon outlawed).

The RAG profiled these engines and noted in particular the very small leading bogie wheels (27" in diameter) and the long piston stroke. At that time the boiler had 258 tubes with a total heating surface of 2,778 sq ft. As with most locomotives, the design gained weight. Originally the adhesion weight was 168,000 lb and the engine grossed an even 100 tons in operating order. The small tender carried 6,000 US gallons of water and 10 tons of coal; the locomotive and tender's total length at that time was 53 ft 7 ".

10 were eventually superheated, and 30 were refitted with Baker valve gear. All were equipped with power reversing gear in the late 1930s.

An M was rated at an even 1,000 tons eastbound from Norfolk to Petersburg and 1,050 westbound.

Class M1 (Locobase 2501)

Data expanded and confirmed by a table in the June 1908 issue of American Engineer and Railroad Journal (p.231).

A follow-on order of "Mollies" produced by Alco-Richmond (50) and Baldwin (50). Thomas Dressler (on notes that these engines were essentially the same as the Ms delivered a year earlier (Locobase 2500) except that they used Walschaert valve gear instead of Stephenson. And therein lay the rub, according to Dressler: "...the centerline of the piston valve was two inches inside the centerline of the cylinders, and a rocker arm was needed to actuate the valve rod. Due to a poor design, scuffing between the link block and face resulted in excessive wear. It was virtually impossible to keep the valve gear in alignment and the valves properly set."

Only one of the 100 received a superheater. Not surprisingly, when the N&W began phasing out older freight power, these M1s were the first to go.

Class M2 (Locobase 939)

Data from DeGolyer, Volume 35, p. 222. Baldwin works numbers for 1101-1149 were 35108-35113, 35146-35149 in August 1910; 35225-35238, 35299 in September; 35331-35345 in October; and

35676-35679, 35774-35775, 35806-35809 in December.

Baldwin-built M2s had Walschaert gear, but the Roanoke-built M2a (3), M2b (2), and the 6 M2c (6) all had Baker gear. Many later received superheaters and mechanical stokers; see Locobase 6654. Arch tubes contributed 13 sq ft to the firebox heating surface area.

Even when upgraded, says Thomas Dressler (, they were "very unpopular" because of their rough riding qualities and poor steaming. The poor steaming -- probably due to a very small firebox heating surface area -- persisted despite substantial modifications to the front end. Most survived until the late 1950s because they were the only non-articulated freight engines the N&W ever had. Their tonnage rating eastbound from Norfolk to Petersburg was 1,750 tons slow freight, 1,850 tons westbound. From Williamson to Portsmouth (Ohio), , an M2 was expected to move 3,600 tons. On a route that included the 0.32% ten-mile Kingston hill between Portsmouth and Joyce, the rating was 3,100 tons.

Farrington (Railroading Coast-to-Coast, 1976) says this was the heaviest Mastodon (4-8-0) class ever built. Two were rebuilt after World War II for yard duties.

Class M2 - superheated (Locobase 6654)

Data from 1955 Norfolk & Western locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

See the full entry at Locobase 939 for this last of the Twelve-wheelers produced for the N & W. Sometime after their introduction, the Roanoake shops overhauled the design by adding superheat. As we note in 939, the crews didn't find much of a difference in the locomotive's performance.

Specifications by Steve Llanso of Sweat House Media
ClassMM1M2M2 - superheated
Locobase ID2500 2501 939 6654
RailroadNorfolk & Western (N&W)Norfolk & Western (N&W)Norfolk & Western (N&W)Norfolk & Western (N&W)
Number in Class1251006161
Road Numbers375-4991000-10991100-11601100-1160
Number Built12510061
Valve GearStephensonWalschaertBaker or WalschaertBaker
Locomotive Length and Weight
Driver Wheelbase (ft)15.5015.501616
Engine Wheelbase (ft)26.4226.4227.0827.08
Ratio of driving wheelbase to overall engine wheebase 0.59 0.59 0.59 0.59
Overall Wheelbase (engine & tender) (ft)58.3753.5861.9662.21
Axle Loading (Maximum Weight per Axle) (lbs)
Weight on Drivers (lbs)169,800165,850221,780239,530
Engine Weight (lbs)206,200204,500261,100279,530
Tender Loaded Weight (lbs)167,500116,600167,500167,500
Total Engine and Tender Weight (lbs)373,700321,100428,600447,030
Tender Water Capacity (gals)9000600090009000
Tender Fuel Capacity (oil/coal) (gals/tons)14101414
Minimum weight of rail (calculated) (lb/yd)716992100
Geometry Relating to Tractive Effort
Driver Diameter (in)56565656
Boiler Pressure (psi)200200200200
High Pressure Cylinders (dia x stroke) (in)21" x 30"21" x 30"24" x 30"24" x 30"
Tractive Effort (lbs)40,16340,16352,45752,457
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.23 4.13 4.23 4.57
Heating Ability
Firebox Area (sq ft)173173192179
Grate Area (sq ft)454544.7045
Evaporative Heating Surface (sq ft)2797279744733586
Superheating Surface (sq ft)765
Combined Heating Surface (sq ft)2797279744734351
Evaporative Heating Surface/Cylinder Volume232.57232.57284.76228.29
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation9000900089409000
Same as above plus superheater percentage90009000894010,620
Same as above but substitute firebox area for grate area34,60034,60038,40042,244
Power L156845684645613,507
Power MT295.20302.23256.71497.27


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