Live Steam Locomotives

Union Pacific 4-6-6-4 Challenger Live Steam Locomotive

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The Union Pacific Challenger:  Our Signature Locomotive

We offer you choices for building your own 7 1⁄4 - 7 1⁄2  inch gauge live steam model of the Union Pacific 4-6-6-4 Challenger:

  • Rough castings
  • Machined castings
  • Machine drawings available with the purchase of our castings
  • Partial construction available: machining and assembly of selected sections
  • Reproductions of original Union Pacific Challenger drawings

Benefits of our Union Pacific Challenger offering:

  • Scaled down from original Union Pacific railroad drawings: Ensures high model accuracy
  • Unique among models: Largest, most powerful and only articulated model on the market
  • Exceptionally high quality product: Fully capable of producing a museum quality model
  • Professionally made patterns and molds: Cleaner, more accurate, beautiful castings
  • Castings made by top commercial foundries: Top quality, fewer casting problems
  • Top quality casting materials: Higher strength, better machinability, better finishes
  • Precision CNC machine work available: Greater accuracy, better finishes, smoother running
  • Hardened and ground parts available: Less wear, longer life expectancy
  • Powder coating available: Long-term protection and durability
  • Partial construction available: Our experience saves you time and guesswork
This model was built from our castings.
Just imagine yourself owning a Challenger like this!

Union Pacific Challenger built from our castings
Challenger locomotive and tender built by our customer Bruno Platzer. Photo by David Lazarus.

"Still being a bit shell shocked and speechless as words are hard to come by at the moment.

I was confident my money was OK and that I was going to receive what I had ordered. However, what has arrived can only be described as the finest set of Model Engineering Locomotive Castings that I have ever seen in 40 years of Model Engineering involvement.

I am a fully indentured Time Served Tool Room Machinist who has spent the first 25 years of my working life working on Military / Aerospace Components then a further 20 years working in the Automotive industry at McLaren Automotive so I regard myself as fairly qualified to comment on the integrity of quality castings.

I can honestly say that the quality and integrity of the castings that you have supplied rivals anything that I ever machined for the Military / Aerospace industry and probably better than anything I have dealt with in the Automotive Industry.

For a very small niche hobby market, you should be VERY, VERY proud of what you have achieved. All the engineers here are so impressed and cannot believe the quality."

- P.F., Shalford, Surrey, England

Proud builder and owner Bruno Platzer pulls the throttle on his completed Challenger.

"I have now had the opportunity to look through the castings. They are absolutely superb. What an achievement to have designed such a complex engine. The tender bed is a work of art even before it is machined. I realized it was a big engine but seeing the parts makes my estimation too conservative! Cannot wait to get started!”
- M.M., Aberdeenshire, Scotland

Union Pacific 4-6-6-4 Challenger Specifications

Drivers: Boxpoc, 8 5/8" Diameter
Cylinder Bore: 2.500" Diameter
Cylinder Stroke: 4.000"
Piston Valves: 1.500" Diameter
Fuel: Builder's Choice, Typically Oil or Propane
Overall Length of Engine & Tender: Approximately 15 1/2 feet
Weight of Engine & Tender: Approximately 2500 lbs.
Minimum Turning Radius: Approximately 60 feet


Union Pacific 4-6-6-4 Challenger Smoke Box and Boiler Specifications

Smoke Box: Conical, 11" Diameter at Front
Boiler: 12" Nominal Diameter (12 3/4" actual OD) x 68 Tubes


Union Pacific 4-6-6-4 Challenger Quality Features

Castings: Top Quality Castings from Top Quality Commercial Foundries
Accuracy: Precision CNC Machine Work Available on Request
Axles: Hardened and Ground
Axle Bearings: Needle Roller Bearings
Crank Pins: Hardened and Ground
Side Rod Bearings: Needle Roller Bearings
Main Rod Bearings: Needle Roller Bearings
Cylinder Blocks: Fully Cored Castings Including All Intake & Exhaust Passages, Very Free Breathing
Valve Gear: Walschaerts
Spring Rigging: Fully Equalized
Brake Rigging: Fully Equalized
Paint: Powder Coating Available on Request


"I opened the boxes of castings, yesterday, and it was better than Christmas! The castings are beautiful and well made. Thank you!" - D.F., Traverse City, MI
We now offer reproduction
Union Pacific Railroad drawings
for the 4-6-6-4 Challenger.

Available only from us:
We are the exclusive source for castings and drawings for building an accurate live steam scale model of the Union Pacific 3900 Series 4-6-6-4 Challenger including the world famous Union Pacific 3985 Challenger steam locomotive and its impressive 14-wheel centipede tender. Union Pacific Challenger 3985 is one of 105 Challengers built for Union Pacific Railroad and is the world's largest and most powerful still operating steam locomotive. UP Challengers were used for both fast freight service (see video) and passenger service. (see video)

Imagine the additional thrill that would come from building an accurate scale model of a locomotive class for which there is still an operating prototype that you can watch on video, visit in-person, photograph in detail and actually ride behind!

Full Size Union Pacific Challenger 3977
Union Pacific 3977
The real thing on display in North Platte, NE Click to enlarge.

Best quality, exceptional accuracy:
Our Challenger is an extremely well engineered and designed model steam engine. The entire design was done on a Computer Aided Design (CAD) system extracting information from the original Union Pacific Railroad drawings for the 3900 class Challenger.

Our patterns and molds have all been made by professional pattern and mold shops. All castings are produced by top quality commercial foundries.

The castings are highly accurate to the prototype design and are of outstanding quality. The castings are fully capable of producing museum quality models. We are frequently told by hobbyists that our Challenger castings are the nicest, most beautiful castings available in the hobby.

Scale Model Union Pacific Challenger 3977
Built by our customer Bruno Platzer. Click to enlarge.

Castings are available in either rough or machined form. Castings may be purchased a few at a time, a section at a time, or all at once.

For customers who order machined castings and/or parts, the machine work is done in our own Computer Numerical Control (CNC) machine shop.


Think you can't build a Challenger?
You just might want to rethink that

We have customers who are building Challengers as their first live steam model locomotive building projects. Some of these customers had no prior machining experience before starting their Challengers but that certainly isn't stopping them.

Here are three real life examples for you to consider before concluding that you could not possibly be able to build your own Challenger:

Example #1:
Bill Dery did not own any machine tools or have any machining experience before starting his Challenger. He purchased a used milling machine and a used lathe and then taught himself how to use both machines while machining castings and parts for his Challenger.

Self-taught machinist Bill shows progress to date
Being built by our customer Bill Dery. Click to enlarge.

Example #2:
Steve Gnas is building a Challenger as his first live steam model locomotive project and is making tremendous progress in record time.

A scale model Challenger under construction
Being built by our customer Steve Gnas. Click to enlarge.

A scale model Challenger is taking shape
Being built by our customer Steve Gnas. Click to enlarge.

Example #3:
Do you think that you would never be able to build a Challenger because you are just too busy? Think again.

Mike Russo is very busy. Yet, he still found a way to build a Challenger as his second live steam locomotive by making the best possible productive use of small increments of spare time. At an overall average of just 30 minutes per day, Mike is turning those small increments of time that would have otherwise been wasted into real progress.

Self-taught machinist Mike shows progress to date
Being built by our customer Mike Russo. Click to enlarge.

Some things for you to consider:
Please keep in mind that aptitude, desire to learn and determination are key ingredients toward being able to build a Challenger and that skills and experience can be developed.

These customers have shown that they are capable of building their own Challengers.

If you have the aptitude, the desire to learn and the determination, then you might also be capable of building your own Challenger.

Roger Goldmann * 413 Morrison Lane. * Santa Paula, CA * 93060 * USA