• An engineer inspects the running gear of a steam locomotive at Steamtown NHS

    Steamtown

    National Historic Site Pennsylvania

Union Pacific 4012: Big Boy

Three quarter view from front right of a large steam locomotive, the Union Pacific 4012 Big Boy built in 1941.

The Big Boy locomotive in Steamtown's collection is on display next to the parking area.  This large locomotive, when running, weighed in at 1,189,500 pounds - just under 600 tons.

NPS Photo, Ken Ganz

Eventually, every railroad faces the same problem: how to move trains over mountains? Small logging and mining railroads purchased geared locomotives - Heislers, Climaxes and Shays - which could pull trains at low speed up steep hills. Medium railroads, like the Delaware, Lackawanna & Western, bought lots of medium-sized engines - 4-6-2s, 4-8-2s and 4-8-4s - and put as many as ten engines on one train. Large railroads like the Union Pacific Railroad, stretching from Kansas City, Missouri and Omaha, Nebraska to Seattle, Washington and Los Angeles, California, preferred a different solution. The Union Pacific ordered larger, more powerful engines such as the 4-12-2 Union Pacific type and 4-6-6-4 Challengers. The trend toward size and power culminated in the 1.2 million pound, 6,200 horsepower 4-8-8-4 Big Boy.

The Big Boys were built for power. They did the work of three smaller engines, pulling 120-car, 3800 ton freight trains at forty miles per hour in the mountains of Utah and Wyoming.

With power, though, comes weight - larger cylinders, pistons, drive rods, boiler and firebox. Steam locomotive manufacturers added more wheels with idlers and powered drive wheels.

The extra wheels added length. Long engines had difficulty squeezing through the sharp track curves, especially in the mountains. A Swiss designer, Anatole Mallet (1837-1919) added a "hinge" to the middle of a locomotive to allow it to "flex" slightly. Two pairs of cylinders supplied power to the two sets of drive wheels.

The Big Boys were built in Schenectady, New York by the American Locomotive Company (ALCO) to the Union Pacific's design. ALCO delivered the first batch of 20 - including #4012 in the Steamtown NHS collection - in 1941 and the remaining 5 in 1944.

Big Boys had over one mile of tubes and flues inside the boiler. Their firebox grate measured 150 square feet. The Big Boys had sixteen drive wheels, each measuring 68 inches. From coupler to coupler they measured 132 feet 9 inches. The tender held 24,000 gallons of water and 28 tons of coal and the engine and tender weighed 1,189,500 pounds in working order. The engines well deserved the name 'Big Boy' which was written on one of the drive rods by an unknown worker at ALCO.

The 25 Big Boys were built to pull long, fast freight trains over the Wasatch Mountains of Utah and Sherman Hill in Wyoming. They served there until 1959 when the new diesel-electric locomotives took over. The Big Boys were not the most powerful engines, though they were the heaviest. But no engine ever came close to matching Big Boy's combination of speed, power and agility. Today, the Union Pacific "Big Boy" #4012 is preserved and on display at Steamtown. Though it does not operate, it remains a most impressive machine.

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Union Pacific "Big Boy" #4014

UP "Big Boy" #4014

Union Pacific Railroad

Union Pacific "Big Boy" #4014

"Union Pacific Railroad announced on July 23, 2013, that it reached an agreement with the Southern California Chapter - Railway & Locomotive Historical Society in Pomona, Calif., to transfer ownership of one of the world's largest steam locomotives, Big Boy No. 4014, back to Union Pacific." [Union Pacific Railroad News Release] Click the image to follow the Union Pacific's progress!


Did You Know?

This small steam locomotive has six wheels and has a water tank above the boiler.  It is called a 'saddle-tank' engine.

This E. J. Lavino & Company locomotive was originally owned by the Poland Springs Railroad, part of the Poland Springs water company of Maine. See this, and more than 20 other steam locomotives, at Steamtown National Historic Site. More...