2-6-6-4 Locomotives in the USA

Most if not all locomotive designs with four-wheel trailing trucks were the result of the desire for more power and the need for a bigger firebox. The 2-6-6-4 design was no different. In 1934 Baldwin constructed three of this wheel arrangement for the P&WV (Pittsburgh & West Virginia) who desired to increase the speed of their freight trains.

This wheel arrangement was made most famous by the Norfolk & Western who perfected this design. The N&W had the most powerful 2-6-6-4s and used roller bearings on the axles. The last five were also equipped with roller bearings on the side and main rods!

High-speed articulateds generally were of two wheel arrangements -- the 2-6-6-4 and the 4-6-6-4. Baldwin was the primary builder of the 2-6-6-4 while ALCO was the primary builder of the 4-6-6-4. In the end, the 4-6-6-4 wheel arrangement became more popular.

A Dimensional Comparison of Large Locomotives

Books and magazines will often state that the Big Boy was the largest steam locomotive ever built. But, what do they mean by "largest"? When comparing steam locomotives, many different quantities can be considered. For example, weight, length, horsepower, and tractive effort are all characteristics of how "large" a steam locomotive is. In many of these categories, a locomotive "larger" than a Big Boy can be found. Does this mean that all of those books and magazines are wrong?

If you were to ignore all of the unsuccessful and experimental locomotives, then look at the overall ratings of the remaining steam locomotives in the above categories, it would become clear that there were many large locomotives. One could argue that the Big Boys were the largest and maybe they were. But the NP Z-5, the DM&IR M-3/4, the C&O H-8, and the N&W Y6b were all examples of the largest of all successful steam locomotives.

ClassZ-5AC-9M-3/M-4EM-1Big Boy (4884-2)M-137AC-10/11/124664-5H-8 - 1645Y6bAQ2S1GL
Wheel Arrangement2-8-8-42-8-8-42-8-8-42-8-8-44-8-8-42-8-8-24-8-8-24-6-6-42-6-6-62-8-8-22-6-6-44-4-6-46-4-4-64-8-2+2-8-4
Cyl:Dia x Stroke26x3224x3226x3224x3223.75x3226x3224x3221x3222.5x3325x3224x3019.75x2822x2622x26
Driver Diameter6363.56364686363.569675870698448
Boiler Pressure250250240235300235250280260300300300300200
Grate Area182139.5125117.5150145139132135106.2122121.713275
Evaporative Heating Surface7,6736,9186,7825,2985,7556,8116,4704,6426,7954,9156,6396,7255,6613,396
Superheater Heating Surface3,2192,8312,7702,1182,0432,1522,6161,7412,9221,4782,7032,9302,085835
Weight on Drivers558,900531,200560,257485,000545,200552,700531,700404,200504,010548,500432,350393,000281,450324,464
Total Engine Weight723,400689,900695,040628,700772,250665,100657,900634,500751,830611,520573,000619,100608,170
Maximum Axle Weight70,90066,40062,10067,80069,08869,10085,48072,00079,78040,992
Tender Weight402,000400,700438,000382,000436,500408,250393,300434,500431,710378,600378,600422,000451,840
Total Engine and Tender Weight1,125,4001,090,6001,133,0401,010,7001,208,7501,073,3501,051,2001,069,0001,183,540990,120951,6001,041,1001,060,010472,864
Overall Wheelbase110.08112.99113.49112.5117.58108112.17106.67112.92114.87108.27107.62123.7683.58
Tractive Effort145,930123,364140,093115,056135,375137,174123,36497,352110,211124,644125,897100,81676,40389,137
Tractive Effort Booster13,40013,90015,000
Maximum Speed8063706050100
Drawbar Horsepower6,345@41.56,000@407,498@465,600@255,300@437,200

Railroads that used 2-6-6-4 Locomotives in the USA (data provided by Steve Llanso of Sweat House Media)

Surviving Examples of 2-6-6-4 Locomotives in the USA

No.ClassF.M. WhyteGaugeRailroad LineLocationStatusBuilder InfoNotes
1218A2-6-6-44'-8½"N&W Virginia Museum of Transportation, Roanoke, VAdisplayN&W #340, 1943 status Operated in Norfolk Southern steam program from 1987 to 1992.
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