UP Railroad "Big Boy" locomotive

This is where my inner 'locomotive archeologist' emerges. A knowlegable railroader cannot possibly find themselves in Wyoming, USA, and not go to the state capital, Cheyenne, to at least see a UP Big Boy locomotive in the park. I was more fortunate; I was able to see and climb onto a fully operational Big Boy (sadly, for me, not in steam... but then you can't have everything!). And, even better, I spent a precious hour with Ed Dickens, the Union Pacific Railroad's Manager of Heritage Operations.

Union Pacific is a Class I freight-hauling railroad that operates (I think) around 4,500 active locomotives (there are many stored) over 32,200 mile routes in 23 U.S. states west of Chicago and New Orleans. The railroad is the second-largest in the United States after the Burlington Northern Santa Fe, which shares a railroad duopoly with UP on transcontinental freight lines in the Western, Midwestern and West South Central United States.

Twenty-five Big Boys were built during World War II, but only eight survive. No. 4014 is now the only one still operational and it remains the world’s largest operating steam locomotive.

Wyoming is special to the Union Pacific system. Big Boy No. 4014 calls the Cheyenne Steam Shop home, as does the railroad's other historic locomotive, No. 844, a big 4-8-4, capable of high speed. Union Pacific has nearly 800 employees in Wyoming.

A Big Boy locomotive is essentially two locomotives in one. Each set of cylinders, drive motion, and wheels constitutes an ‘engine’. The front engine is essentially a separate assembly with a frame that pivots at a hinge that connects it to the rear frame which is located underneath the locomotive's boiler. The hinge, or articulation joint, is positioned where the front set of eight driving wheels meets the rear set of eight driving wheels (i.e. inboard of and between the rear cylinders). This design allows the 133-ft-long locomotive to navigate curves and turnouts, which would be impossible if a single frame of this locomotive’s length were rigid.

Here are some key details of the Big Boy's articulation:
Pivot point location: The pivot is situated between the two sets of eight driving wheels (not at the front of the locomotive). The front pilot truck (or bogie), with its four wheels, is attached to the pivoting front engine frame and helps guide it into curves.
Boiler suspension: The locomotive’s boiler is a single, rigid unit spanning the length of the locomotive. It sits on top of the rear frame and is fixed to it. The front engine unit is articulated and pivots independently of the boiler, therefore the support system must allow for a horizontal sliding motion while bearing immense weight, to permit the front engine unit to move left and right relative to the boiler as the locomotive navigates curved track. A large steel plate, featuring a wide, flat brass surface, is mounted beneath the front of the boiler, below the smokebox. This plate rests on a corresponding surface—the engine frame saddle—on the front engine frame. As the front engine and frame assembly moves from side to side on curvature, the brass plate fixed beneath the smokebox slides across the lower 'saddle' plate that is fixed to the front frame assembly, ensuring the boiler is always supported. Pipes conveying ‘live steam’ from the boiler to the front engine cylinders and then ‘exhaust steam’ from them to the funnel are therefore required to have flexible ball-and-socket articulation joints. I questioned Ed on these joints and he said they do not exhibit a leakage problem.
Reverse shaft: Every steam locomotive has a rod that runs from the engineer’s Reversing lever (sometimes a wheel) along beneath or beside the boiler to the valve motion, whereby the lever can be manipulated to reverse the locomotive or adjust the valve cutoff (i.e. taking account of the expansive qualities of steam) while running. On a Big Boy locomotive, this “reach rod” is required to have a flexible joint to allow for the articulation of the front engine assembly while transmitting movement to the valve gear on the front engine.

Here is my photo essay of my time with a UP Big Boy.En savoir plus