Building a Steam Locomotive in LEGO Part 3 – Scale and Non-LEGO Elements

This is the third installment of a continuing series detailing my progress on modelling the Union Pacific’s 9000 class locomotive in LEGO.


Part 1

Part 2

In this installment, we will discuss the scale my model will use, and why I use it, as well as custom and aftermarket steam locomotive parts.

First, the issue of scale. Model train hobbyists tend to consider scale before anything else because, in general, scale is rigidly established for most model railroads. Most people are familiar with the common model railroad scales, such as HO, O or N. There are countless others,  but they generally have one thing in common – their scale is fixed based upon the track gauge. That is, the distance between the inside edges of the top of the rails. In the LEGO train world, that scale is not so rigidly fixed. LEGO never intended their trains to be part of a model railroad system, so they did not design their track and trains to be in the same scale. The first LEGO train system (not considering earlier wooden and plastic trains without a track system or power) was introduced in 1966. The rails were blue, and the ties white, but the gauge has remained the same in all subsequent LEGO train systems, roughly 38mm. between the inside of the rails. The locomotives and rolling stock were 6 studs wide, roughly 6 feet wide if we considered the rails to be standard gauge. That is obviously not a realistic scale for width but that does not make it somehow ‘wrong’ of course. Many locomotives in the real world are more like 11 feet in width, about 11 studs in LEGO in a strict track gauge equation. There are many excellent models out there in this scale, but it is not typical for a LEGO train layout, and it is not the scale we use in my club.

The issue was further complicated in the 1980s when newer LEGO train systems were combined with the new minifigures. Minifigures were also not scaled with the LEGO track gauge. In fact, all minifigures are less than 5 feet tall to the top of their head stud if we considered the LEGO track to be standard gauge.

Today, the minifigure, more than anything else, determines the scale of many LEGO MOCs, be they models or not, because of the desire to have minifigures be a part of the creation, and because so many other parts like seats, doors, etc. are minifigure-sized. The same seems to hold true for most LEGO train builders. Most individuals and clubs prefer to build trains that work in LEGO layouts involving minifigures, rather than building to a strict track gauge. The result is that there is no one correct scale in the L-gauge world. My club, PennLUG, has a fairly simple scale guideline (not a hard rule) that we use when we are trying to build things to scale with one another. Basically, much of what we build is scaled at .8 studs/ft. With .8 studs being 6.4mm that works out to 1:47.62 in traditional scale terms. I prefer to think of it as .8 studs/ft because feet and inches are usually what is given in American plan drawings, and studs is what I am working with. It’s easier for me to remember.

PennLUG derived that scale from intermodal containers. A few years back, several club members helped me put together an intermodal port module for our layout and part of that was deciding on the standard container sizes. We settled on 32 studs length for a 40 ft container, hence  .8 studs/ft. Interestingly, LEGO used that same size for containers in its original Maersk truck sets from the 1980s.

Proof that LEGO thought of scale at least sometimes.

Many of our subsequent builds have used this scale as a guideline. I say guideline because, of course, exact scale modelling is just not possible in LEGO, at least in smaller scales. The goal is always to build the best model you can within the parameters of the medium.

If I were building say, a boxcar, I would apply the .8 studs/ft scale to the boxcar’s length and height before anything else but, in a steam locomotive, the first thing I consider are the driving wheels. In the past, this issue has been where I usually departed from the .8 studs/ft rule. I always think a model locomotive looks best when the rest of the model is scaled to the drivers. So, I would pick the best driver size based on the available options, and build the rest of the locomotive around it. But, I never found this wholly satisfactory. The problem was that there were a limited number of wheel choices available.

For example, the Union Pacific 9000 had 67″ diameter drivers. That is 4.46 studs, or 35.68mm in our scale. Well, large steam drivers are 30mm in diameter, and Ben Fleskes’ XL drivers are 36mm in diameter. Obviously, XLs are much closer to the right size. They are pretty much a perfect fit, in fact. But they were the largest wheels we had available. What about a big Pacific, or a Hudson, with 80″ wheels? They couldn’t both have XL wheels. They wouldn’t look right next to each other. So, in the past, we would use L wheels for the anything between about 60-72 inches in diameter and XLs for the largest diameter drivers. But this really disrupted our scale. I got so tired of it I finally made my own wheels and had them 3d printed. If you would like some, you can get them here. So now we have XXL wheels, as well as several new smaller sizes. 3d printing may not be perfect, but I am really happy to have this new level of choice in wheel size. With that in mind, using XL wheels for the 9000 was an easy choice. The hard part will be redesigning my older engines to fit different wheel sizes!

The other big issue for locomotive scaling in the LEGO world is width. As stated before, in a strict track gauge, most locomotives work out to 11 studs wide, or even more. That’s bigger than most people build their trains. In PennLUG’s .8 studs/ft standard, locomotives will typically be either 8 or 9 studs wide, depending on prototype size. For larger steam engines, it’s almost always 9 wide for me. There are three main reasons for this. First, it allows the cab to be wide enough for a well-detailed interior seating two minifigs. Second, the cab will be wide enough to provide room for forward windows. Basically, 9-wide lets the cab be proportionately wider than the boiler on large steam locomotives. Finally, I have yet to see a design for cylinders, siderods, etc, that is less than 9 wide. Even LEGO’s Emerald Night is technically 9 wide at the siderods. All the rods and valve gear really add up in width. I find, if the rest of the locomotive is narrower than 8 wide, the running gear really sticks out (both literally and figuratively.) All that said, I can’t say someone building at a different scale is doing something wrong. There are no hard and fast rules. This is just the way I want to build to achieve the result I want to achieve. And that’s the theme of the remainder of this article because a lot of what I am going to put forward is not strictly LEGO building. A lot of rules are bent and broken, and many people may not want anything to do with it. If you’re not too put off by non-LEGO elements in your LEGO models, read on.

If we are being honest, before people started making non-LEGO parts for steam engines, there were very few proper LEGO steam engines: building them was next to impossible. The reason was simple: no drive wheels. All of the standard LEGO train wheels were roughly the same size, about 17mm in diameter. This is a good size for wheels on many diesel or electric locomotives, but rarely suitable for steam. While LEGO made many steam locomotives over the years, only one used a larger wheel size in an attempt at greater realism, 7750 ‘Steam Engine’ from 1980. Still, these wheels were pretty small, and had no way to attach side rods. Also, the set and its wheels are pretty rare today.

LEGO’s best steam engine design for a long time.

This situation changed when Ben Fleskes began selling custom steam drivers. Big Ben’s wheels originally came in two new sizes, medium (24mm diameter) and large (30mm diameter) as well as a small wheel with a Technic axle hole. Ben also more recently added a 36mm XL size. These wheels facilitated steam engine building in a big way. Honestly, there wouldn’t have been many good steam engine MOCs out there without his work. So, as far as purist building is concerned, steam locomotives have basically fallen outside that category for a very long time. Of course, LEGO’s Emerald Night finally added some stock train wheels to our toolbox, but it is still only one size. I still largely rely on Ben Fleskes’ wheels, as do many other train builders.

As I said above, I wanted to use XL wheels for the UP 9000. This is because I have begun designing and printing my own wheels in several more sizes. The availability of an XXL size makes it feasible for me to use XLs on this model, while still having larger wheels available for engines with much larger drivers. While the prints do not have the same high quality finish you can get from Ben Fleskes’ molded wheels, the advantage lies in being able to make as many variants as you like without a huge upfront cost. So, even though Ben’s XL wheels already existed, I figured I would make my own wheels for the 9000, based on the actual design of its drivers.

It looks a lot like Ben’s XL driver, but it has 15 spokes instead of 16. LEGO train builders may not be ‘rivet counters,’ but I’m at least a spoke counter.

The 9000 class had 12 drive wheels and, for my model, each wheel is unique. There are two main reasons for this. First off, each driving axle had wheels with a different-sized counterweight. This was necessary to properly balance out the reciprocating weight of the siderods, and the center axle crank. Additionally, beginning in 1936, Union Pacific had Boxpok type drivers made for many of their locomotives, including the 9000 class. Their design provides improved counterbalancing, which makes the locomotive ride more smoothly and theoretically extends time between certain maintenance operations. However, they decided it wasn’t worth the cost to replace all 12 drivers on the 9000s with Boxpok types. Only the main axles, the axles directly receiving the power from the cylinders, would get this upgrade.

For most locomotives, that would be a single axle, the one where the piston rods connect to the side rods, but the 9000 class’ center cylinder crank connected to the second axle, while the outside rods connected to the third axle. So the 9000s had two ‘main’ axles. Both received an upgraded wheel design, though these were only added during regular shoppings when a wheel replacement was needed and, even then, if stores of spoked wheels were on hand, these would be used. As a result, an engine might go back and forth several times between spoked and Boxpok wheels in its service lifetime. The surviving 9000 does not have Boxpok wheels, though earlier pictures show that it did at some point in the past. At any rate, I wanted the Boxpok wheels for my second and third axle, because it tells more of the story of this class of engine, and the variety of wheels is visually interesting. Boxpok wheels are a little more complex to design, as they are often not symmetrical.

Thankfully, I have access to images of the original plans.

Second axle Boxpok design. The counterweight is off center because this wheel has to counterbalance the center crank and the siderods.
Third axle Boxpok design. This wheel has the largest counterweight, as it must balance the weight of the piston rod.

Now I said above that all twelve wheels on my 9000 are unique, which means even the left and right driver on the same axle are a different model. The reason for this is that the 9000 was a 3 cylinder engine. For most steam engines, the drivers are ‘quartered’ to properly distribute the power strokes of the cylinders to the wheels. Steam pistons provide power both when they are pushing forward and backward. So, two power strokes per cylinder and two cylinders means four power strokes. If the drivers on one side of the locomotive are offset 90 degrees from the ones on the other side, you will have one power stroke every 90 degrees of wheel travel; four per rotation. On a three cylinder locomotive, you have 6 power strokes. In order to distribute them evenly throughout a full wheel rotation, the drivers are ‘thirded,’ offset by 120 degrees. The center axle crank is also offset 120 degrees. The result is a power stroke every 60 degrees of wheel travel. I wanted to model this effect, but it’s difficult with the way Big Ben and LEGO steam drivers attach, using a Technic axle. Technic axles only allow for offsets of 90 or 180 degrees. To get 120, I designed all of the drivers for one side of the 9000 with normal looking Technic axle holes, but those on the opposite side had the axle holes offset 30 degrees. Here is what that looks like:

My design for the axle 2 Boxpok driver. They are identical except the orientation of the axle hole.

None of this would have been realistic to do without 3d printing technology. I can make as many variations as I like.

All 12 custom UP 9000 drivers

Additionally, I wanted a custom wheel for the pony truck. Like many steam engines, the 9000 class had a fairly large wheel under the firebox. The pilot truck wheels are 30″ in diameter, and standard LEGO train wheels are perfect for this size, but the pony truck wheels were 45″. This works out to 3 studs in my scale, or 24mm. Perfect for a Big Ben medium sized wheel. But, I wanted it to be thin, like the pilot truck wheels, and have the right number of spokes, of course, so I made my own.

Plan for UP 9000;s pony truck wheel.
My design is a cross between the prototype and a standard LEGO train wheel.

As far as wheels go, the only other non-LEGO feature are the ball bearings I used under the tender. We have a write-up of the bearing technique here. This was my first time working with these bearings, so I thought I would share my experience and some tricks I learned. First, it is extremely important that, if you have two bearings in two separate pieces holding the axle, that those two bearings be as parallel to one another as possible. Even a small error here will cause the wheels to perform poorly. Check and recheck the bearings as you work with them! Second, you need some sort of bushing between the bearing and the wheel. If the wheel slides all the way over in one direction or the other, it will rub on the side of your frame, or against the bearing, and you will have problems. I’ve been using small pieces of LEGO 3mm tubing for bushings, and that has helped out a lot. My run tests have been positive with the bearings so far, but I have yet to use them at a show for extended periods of time. If I learn anything else, I will share it in a future post.

There are really only two parts of this project where I wanted to use non-LEGO elements. The wheels were the first, and most obvious, but the rods and valve gear are also really improved by moving away from pure LEGO. For years, LEGO train builders struggled to make realistic looking siderods and valve gear. It is certainly possible to do if you are making a large-scale engine, but at some version of minifigure scale, like I am working with here, I honestly think it’s impossible. The problem is width. First of all, as we established above, even a big 9-wide engine really isn’t scaled to the track gauge. As a result, the wheels are farther from the centerline of our model locomotives than they would be in reality. The wheels are already 6 wide! We’re running out of room and we haven’t even added anything yet. At a minimum, siderods would be .5 studs thick, using thin Technic liftarms. But you can’t really use a single thin liftarm for long wheelbases. You have to connect multiple thin liftarms together, so now they are 1 stud thick each. We are at 8 wide total now. A thin liftarm for the piston rod gets you to 9 wide. Where does the valve gear go? You would easily get to 12 wide or more trying to build it out. Especially on large locomotives like the UP 9000, I have never seen a satisfactory stock LEGO solution to this problem.

Thankfully, I don’t worry about that anymore, thanks to fellow LEGO train builder Benn Coifman. He has started designing and 3d printing side rods and valve gear in every size. He even takes requests for custom sizes that he has not already made. This was especially important for the 9000, which has 6 axle side rods where the distance between the first and second axle holes is greater than all the others. On the real engine, this provided clearance for the center crankshaft to the second axle, and it’s a very obvious visual feature of the engine. He was able to make me exactly what I needed. Without his parts, I could never do what I wanted to do with the 9000.

The siderods Benn made for the 9000

His side rods also gave me the confidence to start working with the 3d printed wheels. I had been worried that the 3d printed plastic, made from sintered plastic powder, would be too weak or brittle to stand up to use on a working LEGO steam engine. As it turned out, they are more than strong enough. I have been using them for years now and have never broken one.

There are two parts of a complete valve gear system that Benn does not currently make. First, there is the eccentric crank; the part that offsets the valve gear rods from the main piston rods. The second is a way to connect the valve gear pieces together. There are certainly stock ways to connect the valve gear pieces, but I often find they allow too much play in the valve gear, or that the connectors stick out too much and interfere with other parts of the running gear. So, I made some parts myself.

Eccentric crank pieces. The pin on the bottom (right piece in the picture) sticks into the Technic pin holding the side rods together. The socket side accepts a pin, and holds on a valve gear piece.
Pin pieces with Benn’s valve gear parts to show how they are meant to work.

I don’t offer these for sale, and perhaps this is why Benn doesn’t either, because they tend not to fit together properly out of the box. I have tried many different sizes for the pins and sockets on these parts, and find the best solution to a good fit is to design the pins to be too thick, and then sand them a bit. Not ideal, but it works well enough for my purposes. Also, as Shapeways does not offer a color close enough to LEGO light bley, these parts will need to be painted. I will talk about the paint I use when I, well, figure that out.

For any other engine project, I would have stopped my discussion of custom parts there, but the 9000, as a three cylinder locomotive, had some features that few other locomotives had. First, there was the center cylinder crank. For the crankshaft, itself, I used one of Benn’s side rods, but, as you can see below, in order to be cranked, the second axle had to be made in two pieces, with a counterweighted crank attachment point. These crank pieces were unique enough that I decided to make my own. This was not only to make something that looked more like the prototype, but to provide the necessary 30 degree offset in the axle hole for the driver ‘thirding.’



UP 9000 second cranked axle

My custom counterweight comes in two types. One has a socket, and the other a pin.

Even more necessary is the last piece of the three cylinder puzzle, the valve linkage to the center cylinder. Steam locomotive valve gear ensures that the valve movements remain properly timed to the rotation of the wheels and movements of the pistons. It is an essential part of steam locomotive design, and it is especially complicated when a third cylinder is involved. There are lots of ways to potentially actuate a center cylinder. Union Pacific and the 9000’s builder, Alco, chose the Gresley Conjugating Lever. Check the link for more information, but the short explanation is that the Gresley lever uses the motion of the outside two valves to time the movement of the middle valve. It has the advantage of being entirely on the outside of the locomotive frame, and so it is easier to maintain. Alco had exclusive rights to this design in the United States, and sold it enthusiastically to its customers. They were so interested in getting buyers, that they made a small motorized model of the 9000’s running gear to show to customers.

Alco’s 3 cylinder model

The two pieces of the Gresley gear are really prominent on the prototype, and I wanted them to actually work. I decided custom pieces would be the best solution to achieve both the correct form and function.

This picture of the surviving 9000 prominently shows the Gesley Gear just above the pilot beam.
Plans for UP 9000 Gresley parts


My Gresley part prints

I do think that the Gresley gear action could be modeled in a stock LEGO way, but not in the small available space. I could also have made one that looks pretty good in LEGO at the right size, but didn’t work. Perhaps all these custom parts are taking it too far. Honestly, I doubt I will go to this level of trouble for every locomotive I build, but I really wanted to showcase with the model 9000 what the possibilities for building a LEGO steam engine really are, both in terms of what can be done with the brick, and with some of the new aftermarket options that are out there. And, in the end, this is the engine that I want to build, and the way I want to build it, pure or not.

Between the electronics I discussed in the previous article, and custom pieces above, that is all of the non-LEGO components for my 9000 model. Nevertheless, there is another non-LEGO element that is making this design possible – the track. Now, to be clear, my 9000 runs on standard LEGO track geometry. Curves, switches, you name it.

Every locomotive I build meets that basic requirement (though their switch success rate is not always 100%). It can handle standard LEGO track, but it won’t actually have to very often in its operational life, because of all the new aftermarket track options out there. Glenn Holland covered these in some detail here so I won’t go through it all again. Suffice it to say that an engine like the 9000 looks kind of dumb in a standard curve, and it’s really hard on the battery. It’s also extremely difficult to pull long, heavy consists though tight turns like that. I have tried a couple engines with long, rigid wheelbases over the years, including a previous stab at the 9000, and they have always performed poorly, in part due to the track geometry issue. I am very excited to be able to run the new 9000 on grand curves. But first, I need to actually finish it.

Next time we will cover some real, honest-to-goodness building. Part 4 will cover the design of a steam locomotive frame, the articulation of the drivers, pilot and pony truck, and techniques for mounting motors. Stay tuned!

5 thoughts on “Building a Steam Locomotive in LEGO Part 3 – Scale and Non-LEGO Elements”

  1. Great Job! Love these articles! I have a question though: I am actually in the process of modeling this very engine in Lego (after being inspired by your work and that of Jason Steinhurst in modeling this engine) and was wondering if you could send me scans of the portions of those two books on the UP Type specifically that contain the measurements of the wheels and the valve gear, since in building my model my anchor measurement is track gauge, and thus my wheels will be considerably bigger at 47.4 mm. I’d ask to borrow both books in their entirety but since you’re not a public library, and as we have never actually met and as such there is no basis of trust or mutual understanding between us, I figured this would be a bit of a stretch. Keep up the great work! I look forward to reading the next article in the series!

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