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.

ClassM-137Y6bR-2Z-5AC-9M-3/M-4EM-1AC-10/11/12Big Boy (4884-2)4664-5H-8 - 1645AQ2S1GL
Wheel Arrangement2-8-8-22-8-8-22-8-8-22-8-8-42-8-8-42-8-8-42-8-8-44-8-8-24-8-8-44-6-6-42-6-6-62-6-6-44-4-6-46-4-4-64-8-2+2-8-4
Cyl:Dia x Stroke26x3225x3228x3226x3224x3226x3224x3224x3223.75x3221x3222.5x3324x3019.75x2822x2622x26
Driver Diameter6358636363.5636463.568696770698448
Boiler Pressure235300240250250240235250300280260300300300200
Grate Area145106.2126182139.5125117.5139150132135122121.713275
Evaporative Heating Surface6,8114,9157,8697,6736,9186,7825,2986,4705,7554,6426,7956,6396,7255,6613,396
Superheater Heating Surface2,1521,4783,5153,2192,8312,7702,1182,6162,0431,7412,9222,7032,9302,085835
Weight on Drivers552,700548,500544,000558,900531,200560,257485,000531,700545,200404,200504,010432,350393,000281,450324,464
Total Engine Weight665,100611,520630,750723,400689,900695,040628,700657,900772,250634,500751,830573,000619,100608,170
Maximum Axle Weight69,08868,00070,90066,40062,10069,10067,80085,48072,00079,78040,992
Tender Weight408,250378,600372,780402,000400,700438,000382,000393,300436,500434,500431,710378,600422,000451,840
Total Engine and Tender Weight1,073,350990,1201,003,5301,125,4001,090,6001,133,0401,010,7001,051,2001,208,7501,069,0001,183,540951,6001,041,1001,060,010472,864
Overall Wheelbase108114.87106.02110.08112.99113.49112.5112.17117.58106.67112.92108.27107.62123.7683.58
Tractive Effort137,174124,644162,475145,930123,364140,093115,056123,364135,37597,352110,211125,897100,81676,40389,137
Tractive Effort Booster13,90013,40015,000
Maximum Speed5063807060100
Drawbar Horsepower5,600@256,000@406,345@41.57,498@465,300@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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