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Bowser - HO - Steam Loco Kits
Union Pacific Big Boy 4-8-8-4

History:  The Union Pacific 4-8-8-4 "Big Boy" are considered to be the longest and heaviest locomotives built by Alco. They were designed in 1941 and 1944 to conquer the grade between Ogden and Evanston through the Wasatch Mountains.

This design utilized lateral motion devices, and were able to run as fast as 80 miles per hour, but their best horsepower was at 30 miles per hour. The engines had 23 3/4" x 32" cylinders, 68" drivers, used 300 pounds of boiler pressure and weighed 772,000 pounds. Twenty engines were originally ordered in 1941. These were engine numbers 4000 to 4019. Five more engines were eventually ordered in 1944. These were numbered 4020 to 4024.

Around September 10, 1941 the 4000 was tested on the grade that it had been built to beat. It was hauling a 3800 ton train and made the 65 mile plus trip into Wahsatch and on to Evanston ahead of the photographer.

Fittings were added, including twin stacks hidden behind a sheet-metal fence and equipped with side-folding smoke hoods. Feedwater was heated with an Elesco exhaust injector combined with a centrifugal pump. The engines were used as coal-burners. Big Boys first used air cooling piping supported lengthwise on each side of the pilot deck and later used Wilson after-cooled radiators as on the Challenger series.

The Big Boys were the King of steam for eighteen years, but they might not have ever been built, for while the 4000 series were in the design stage, deisels were being tested experimentally throughtout the nation.

A word of advice - this loco kit is not a beginner's kit.  After all, this is a hobby.  In order to enjoy building kits, we suggest that you build at least 2 other Bowser kits before you try the Big Boy.  In addition to complexity, we make the body by cutting two Challenger boilers and soldering them together.  As a result, this kit requires patience and some assembly experience to build it, and a lot of filling to smooth the joining seam.

Complete Kit and Accessories:  The locomotive and tender complete kit has all of the parts to build a working model. You may wish to add your own details or purchase our "Super Detail Kit" if available. Some models have an optional painted engineer and fireman, smoke unit kit and other assemblies available as optional equipment to compliment your kit-building needs.

Part #DescriptionPrice
1-100350   Big Boy Kit * n.a.
1-100375   Big Boy Super Detail Kit * n.a.
1-150001  Semi-Vanderbilt SP-1 Tender * n.a.
1-150650  Long Haul Tender Kit * n.a.
1-150681   Electrical Kit Mono 14 Wheel Tender * n.a.
635-2291  Union Pacific Centipede Tender - Coal * n.a.
635-2292  Union Pacific Centipede Tender - Oil * n.a.

Kit Components and Replacement Parts:  The following parts are listed in order to identify parts in your kit or to replace parts that have been lost, damaged or simply worn out.  This is not a complete list of all of the individual parts available for this model - please call Bowser with your specific requirements if you cannot find the parts you need.  You may also use our on-line catalog to find parts by description.  Please note that part numbers with a price of "Call Us" may be part of an assembly and may not be available as a separate purchase item.

Part #DescriptionPrice
1-100304  Lead Truck Kit ARC-1 (included in Kit), K-3004 * n.a.
1-100310  Bell Kit, Challenger/Big Boy, K3010 (included in Kit) * n.a.
1-100311  Trailing Truck Kit, Challenger/Big Boy K3011 (included in Kit) * n.a.
1-100322  Crosshead Guide Support Kit (included in Kit) * n.a.
1-100323  Drawbar Kit for Challenger/Big Boy (included in Kit) * n.a.
1-100351  Big Boy Side Rod Kit (included in Kit) * n.a.
1-100352  Big Boy Worm Mount Kit (included in Kit) * n.a.
1-100353  Big Boy Miscellaneous Kit (included in Kit) * n.a.
1-100355  Big Boy Valve Gear Kit (included in Kit) * n.a.
1-100356  Big Boy Castings Kit (included in Kit) * n.a.
1-100357   Big Boy Front Frame Kit (included in Kit) * n.a.
1-100358   Big Boy Rear Frame Kit (included in Kit) * n.a.
1-100359  Big Boy Steam Pipe Kit (included in Kit) * n.a.
1-100364   Big Boy Pilot Assembly Kit (included in Kit) * n.a.
1-100369   Big Boy Mechanism Kit (included in Kit) * n.a.
1-100370  Big Boy Instructions (included in Kit) [also a 1.4Mb PDF] * n.a.
1-100371  Boiler, Frame, Drivers, Tender, Trucks (included in Kit) * n.a.
1-100372   Big Boy Crosshead Guide Support Kit (included in Kit) * n.a.

  Builder Alco
  Tractive Force 135,375 pounds
  Drivers 68"
  Engine Weight 772,000 pounds
  Engine wheel base 72' 5-1/2"
  Steam Pressure 300 pounds
  Height 16' 2-1/2"
  Length 85' 9-1/2"
  Drivers 69" Box Pok
  Gear Ratio 31 - 1
  Power DC-71 motor
  Boiler length 12-1/4"
  Engine height 2-1/4"
  Overall length 18-5/8"
    w/ centipede tender
  (From inside of Outside Rail)
  18"Radius Curve 1.688"
  20"Radius Curve 1.437"
  22"Radius Curve 1.375"
  24"Radius Curve 1.250"

  NOTE: If curves are given the
  clearance as outlined in NMRA
  standards, no difficulty with
  overhang will be encountered.

Parts List:  List of parts included in Bowser's Big Boy Super Detail Kit (see parts list above)