Union Pacific Big Boy

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Union Pacific Big Boy
UP Big Boy 4014.jpg
Big Boy 4014 on display in Pomona, California
Type and origin
Power type Steam
Builder American Locomotive Company
Build date 1941 (20), 1944 (5)
Total produced 25
Configuration 4-8-8-4
UIC classification (2′D)D2′ h4
Gauge 4 ft 8 12 in (1,435 mm) standard gauge
Leading wheel
36 in (914 mm)
Driver diameter 68 in (1,727 mm)
Trailing wheel
42 in (1,067 mm)
Wheelbase 72 ft 5.5 in (22.09 m)
Length Locomotive: 85 ft 3.4 in (25.99 m)
Overall: 132 ft 9 14 in (40.47 m)
Width 11 ft (3.4 m)
Height 16 ft 2 12 in (4.94 m)
Weight on drivers 540,000 lb (244,939.9 kilograms)
Locomotive weight 762,000 lb (345,637.4 kilograms)
Tender weight 342,200 lb (155,219.3 kilograms) (2/3 load)
Locomotive and tender
combined weight
1,250,000 lb (566,990.5 kilograms)
Fuel type Coal
Fuel capacity 28 short tons (25.4 t; 25.0 long tons)
Water capacity 25,000 US gal (95,000 l; 21,000 imp gal)
Boiler 95 in (2,400 mm)
Boiler pressure 300 lbf/in2 (2.1 MPa)
Firegrate area 150 sq ft (14 m2)
Heating surface:
– Tubes and flues
5,035 sq ft (468 m2)
– Firebox 720 sq ft (67 m2)
– Total 5,735 sq ft (533 m2)
Superheater type Type A
Superheater area 2,043 sq ft (190 m2)
Cylinders 4
Cylinder size 23.75 in × 32 in (603 mm × 813 mm)
Performance figures
Maximum speed 80 mph (130 km/h)[2]
Tractive effort 135,375 lbf (602.18 kN)
Factor of
Operator(s) Union Pacific Railroad
Class 4000–4019: 4884-1
4020–4024: 4884-2
Last run July 21, 1959
Preserved 4004, 4005, 4006, 4012, 4014, 4017, 4018, 4023

17 scrapped, seven on display at different places, one (4014) undergoing restoration.

4014 was reacquired by Union Pacific and is being restored to operating condition.

Big Boy is the popular name of the American Locomotive Company 4000-class 4-8-8-4 articulated, coal-fired, steam locomotives manufactured between 1941 and 1944 and operated by the Union Pacific Railroad until 1959. The Big Boy fleet totaled twenty five locomotives that were used primarily in the Wyoming Division to haul freight over the Wasatch range between Green River, Wyoming and Ogden, Utah. The Big Boy locomotives were the only locomotives to use a 4-8-8-4 wheel arrangement, consisting of a four-wheel leading truck for stability entering curves, two sets of eight driving wheels and a four-wheel trailing truck to support the large firebox.

According to Ed Dickens Jr., Union Pacific's senior manager of heritage operations, the legendary name was coined by an unknown worker who scrawled "Big Boy" in chalk on the front of one of the engines as it was being built. The original name of the locomotive were to be "Wasatch". "Big Boy" became the name of the locomotive thereafter.[2]


Big Boy 4006 on display at the Museum of Transportation, outside St. Louis, Missouri

Union Pacific introduced the Challenger-type (4-6-6-4) locomotives in 1936 on its main line over the Wasatch Range between Green River, Wyoming and Ogden, Utah. For most of the route, the maximum grade is 0.82% in either direction, but the climb eastward from Ogden, Utah into the Wasatch Range reached 1.14%. Hauling a 3,600-short-ton (3,300 t; 3,200-long-ton) freight train demanded doubleheading and helper operations, and adding and removing helper engines slowed operations.

To eliminate the need for doubleheading and helper operations, Union Pacific decided to design a new locomotive. For such a locomotive to be worthwhile, it would have to be faster and more powerful than slower locomotives like earlier compound 2-8-8-0s that UP tried after World War I. To avoid locomotive changes, the new class would need to pull long trains at a sustained speed of 60 miles per hour (100 km/h) once past mountain grades. In fact, it was designed so that it could travel at 80 miles per hour (130 km/h) — even though it was not intended to be used that fast — the point being that at 80 mph, it could operate smoothly, and not pound itself to pieces.[2]

Led by mechanic Otto Jabelmann, the Union Pacific Railroad's design team worked with the American Locomotive Company to re-examine their Challenger locomotives. The team found that Union Pacific's goals could be achieved by making several changes to the Challenger design, including enlarging the firebox to approximately 235 by 96 inches (5.97 m × 2.44 m) (about 155 sq ft or 14.4 m2), lengthening the boiler, adding four driving wheels and reducing the size of the driving wheels from 69 to 68 in (1,753 to 1,727 mm).

The Big Boys are articulated, like the Mallet locomotive design. They were designed for stability at 60 miles per hour (100 km/h). They were built with a wide margin of reliability and safety, as they normally operated well below that speed in freight service. Peak horsepower was reached at about 35 mph (56 km/h); optimal tractive effort, at about 10 mph (16 km/h).

Without the tender, the Big Boy had the longest engine body of any reciprocating steam locomotive.


The American Locomotive Company manufactured 25 Big Boy locomotives for Union Pacific; two groups of ten in 1941 and one group of five in 1944.


The backhead (controls) of 4017 at the National Railroad Museum in Green Bay, Wisconsin

The Big Boy locomotives burned coal and had large grates to burn the low-quality bituminous coal sourced from Union Pacific-owned mines in Wyoming.

As an experiment, Locomotive 4005 was converted to burn oil, but unlike a similar effort with the Challengers, this was not successful, and the locomotive was changed back to coal. The cited reason for this failure was the use of a single burner, which created uneven heating in the Big Boy's large firebox.

Postwar increases in the price of both coal and labor and the efficiency of diesel-electric motive power foretold a limited life for the Big Boys, but they were among the last steam locomotives taken out of service. Towards the end of their career, the Big Boys could still pull more than their rated tonnage of 6,573 tons (6,573 t). The Big Boys ratings were increased several times until they regularly pulled 8,727 short tons (7,917 t) over the Wasatch range.

The last revenue train hauled by a Big Boy ended its run early in the morning on July 21, 1959. Most were stored operational until 1961, and four remained in operational condition at Green River, Wyoming until 1962. Their duties were assumed by diesel locomotives and gas turbine-electric locomotives.


Of the 25 Big Boy locomotives manufactured, eight remain. Seven of the eight surviving Big Boys are on static display. One, number 4014, is undergoing a restoration for excursion service which includes conversion to No. 5 oil firing. Five are displayed outdoors without protection from the elements; 4005 and 4017 are displayed indoors. The remaining Big Boy locomotives are located throughout the United States:

Restoration of 4014[edit]

In late 2012, Union Pacific announced that it was interested in acquiring a Big Boy to be restored and then operated in excursion service.[2][5]

On July 23, 2013 Union Pacific announced that it has acquired 4014 from The Southern California Chapter of The Railway and Locomotive Historical Society in Pomona, California. Union Pacific began inspecting and preparing to move 4014 from Pomona to Union Pacific's Steam Shop in Cheyenne, Wyoming in August 2013. Movement commenced on 14 November. Now back in Cheyenne, Union Pacific's Heritage Fleet Operations team is restoring 4014 to operating condition, which is expected to take three to five years.[6] As part of the restoration process, Union Pacific will convert 4014 from coal to No. 5 oil firing.[7]

As of November 12, 2013 U.P. Heritage Fleet Operations director Ed Dickens reported via his official YouTube channel that UP4014 was prepared for the move, and track laying was in progress. Several issues delayed the connection of the display track to the temporary rails. Crews used creative and classic methods, including plywood supports and "dutchman compromise joints"[A] to solve uneven surfaces, a 1% grade, and several difficult curves.

On the morning of January 26, 2014, UPP 4014 (recently re-numbered on the U.P. active locomotive roster so as to avoid confusion with UP 4014, a diesel locomotive) was pulled out of the Los Angeles County Fairplex by a 4,300 horsepower Union Pacific diesel locomotive. The Fairplex property had been the Big Boy's home for 52 years where it was displayed on a track managed by The Southern California Chapter of the Railway and Locomotive Historical Society. UPP 4014's ultimate destination for restoration to full operating condition was the Union Pacific Steam Shop in Cheyenne, Wyoming[8] under the guidance of Heritage Fleet Operations director Ed Dickens. The Big Boy left UP's West Colton yard on its journey to Cheyenne, Wyoming on April 28, 2014 and arrived in Cheyenne on May 8, 2014.[9]

In Fiction[edit]

In the anime series The Galaxy Railways, the locomotive Big One is represented by a UP Big Boy.



  1. ^ The Dutchman compromise joint is a variation of the simple bar joint. It is an offset or step joint used for joining two rails of different sizes, weights or shapes "Other Track Material and Accessories" (PDF). L.B. Foster. Retrieved April 15, 2014.  "Compromise Joints - tr067080075 - Army Transportation". tpub.com. Retrieved April 15, 2014. 


  1. ^ Peck, Combes & Augur 1950, pp. 501,519,523,545.
  2. ^ a b c d Elliott, Dan (April 15, 2014). "Huge Big Boy steam locomotive coming back to life". Yahoo! News. Associated Press. Retrieved April 15, 2014. 
  3. ^ a b c Chappell, Gordon. "Union Pacific No. 4012". Steam Over Scranton: Special History Study, American Steam Locomotives. National Park Service. Retrieved March 13, 2012. 
  4. ^ "Steamtown's Locomotives and Cars". Steamtown National Historic Site. National Park Service. Retrieved March 13, 2012. 
  5. ^ "Union Pacific Looking To Restore Big Boy for Excursion Service". Trains (Kalmbach Publishing Co.). 2012-12-07. Retrieved 2012-12-08. 
  6. ^ "Union Pacific Railroad Acquires Big Boy Locomotive No. 4014" (Press release). Union Pacific Railroad Company. 2013-07-23. Retrieved 2013-10-28. 
  7. ^ "Big Boy No. 4014". Union Pacific Railroad Company. 2012. Retrieved 2013-07-23. 
  8. ^ "Big Boy steam locomotive begins trip from California to Wyoming; will return to the rails". 2014-01-26. Retrieved 2014-01-26. 
  9. ^ http://www.up.com/aboutup/special_trains/steam/locomotives/4014/index.shtml


  • Peck, C. B.; Combes, C. L. et al., eds. (1950). 1950-52 Locomotive Cyclopedia of American Practice (Fourteenth ed.). New York: Simmons-Boardman Publishing. ASIN B009AF0VKU. 

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