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The Worlds Largest Operating Steam Locomotive stokes up her big boiler for maximum steam pressure for an eastbound trip to Omaha Nebraska
on Sept. 18, 2008
UP 3985 operated in its last "regular" train service in 1957. The locomotive was retired about 1962 and after many years of storage in a roundhouse at Cheyenne, Wyoming. UP 3985 was placed on outdoor display beside the Cheyenne depot in 1975. Beginning in 1979 a group of Union Pacific employee-volunteers started work on overhauling the locomotive, and it was returned to operational condition in 1981. Originally a coal-burner, to prevent lineside grass fires it was successfully converted to oil firing in 1990. Stationed at Cheyenne with other equipment in the UP's heritage collection, it is currently used for excursion trains and occasionally mainline freight on ferry moves. It was in the maintenance shop at Cheyenne in 2007 and underwent necessary repairs for service in 2008. It is now back up and running as of 2008. It is one of only two of the original 105 Union Pacific "Challenger" types in existence, the other being UP 3977 on static display in North Platte, Nebraska.
info on 4-6-6-4 at
Union Pacific Challenger No. 3985 was designed by Union Pacific and built in 1943 by the American Locomotive Company. It is one of 105 Challengers built for Union Pacific between 1936 and 1943 and is the only operating engine of its class in the world today the largest and most powerful operating steam locomotive.
No. 3985 last operated in "regular" train service in 1957. It was retired in 1962 and stored in the roundhouse in Cheyenne, Wyoming, until 1975 when it was placed on display near the Cheyenne depot. A group of Union Pacific employees volunteered their services to restore the locomotive to running condition in 1981.
The name Challenger was given to steam locomotives with a 4-6-6-4 wheel arrangement. This means that they have four wheels in the leading "pilot" truck, which helps guide the locomotive into curves; two sets of six "driving" wheels, and finally, four "trailing" wheels, which support the rear of the engine and its massive firebox. Each set of driving wheels has its own steam cylinder. In essence, the result is two engines under one boiler.
The frame of the locomotive is "articulated," or hinged, to allow it to go through curves. When watching the approaching locomotive go through a curve, you can see the boiler swing out left or right independently of the lower half of the engine, as the rear half of the locomotive remains in a straight direction until its wheels and frame are halfway through the curve.
The Challengers were designed for fast freight service, but occasionally pulled passenger trains. No. 3985 originally burned coal and pulled a tender with a 32-ton capacity. In 1990, it was converted to use No. 5 oil. The top speed of No. 3985 is about 70 m