sets instructions boxes stickers minifigs
articles library mocs apps

12v Steam Engine

Steam Locomotive
413 pieces, 1 minifig

Fouke Boss
January 2023


As a kid, I was lucky to own several sets of grey-era LEGO trains, including 7710, 7740, and 7834. One set I never had though was the 7750 Steam Engine, and I certainly never had the parts to complete the big steam locomotive of ideas book 7777. My dad got me the big red wheels service pack 1143, but due to lack of parts, that's as far as I got.

Now in recent years, I've started collecting the 12v grey era trains, and so the 7750 and 7777 steam engines regained my interest. I have however started noticing how both engines look a bit clunky and perhaps are not the best recreations of the great German steam engines from the first half of the 20th century.

And so I started designing a big steam engine of my own. Starting point was the general LEGO steam engine design of the 1980s, of course like sets 7750 and 7777, but also 7710 and 7810. With the bricks available in 1980, what could set 7750 have looked like if Lego had taken a better look at those big German steam engines?


As a real-life prototype, I settled on the Deutsche Bahn Baureihe 41. The main elements that I wanted to incorporate include the 2-8-2 wheel arrangement, the fact that the top of the main tank is almost at the same level as the top of the cab, the location of the plateau underneath the main tank (which is way higher than the base of the cab), the design of the leading bogie, the closeness of the cab and the tender, and the size and location of the steam domes and chimney.

Deutsche Bahn, Baureihe 41

But above all, I wanted to retain that 1980s LEGO trains look and feel. After much trial and error, and much experimenting, I came up with this design:

The design combines the design features of the 7750 (the tubes on the main tank, the use of all those very specific and expensive 7750 parts, the stickers), the 7777 (the tender, the smoke deflectors, the lights in the tender and locomotive), the 7810 (the 2x2x3 slopes and the design of the cab with the open back) and the 7710 (general design of the main tank). The steam engine has exactly the same length as the 7740 locomotive.

Comparison to the original 7750

Wheel arrangement

One of the more challenging areas of the design is the wheels and bogies. It took several attempts to arrange the wheels in such a way that the engine never hits other trains or the points control box (as does 7750) and the wheels run freely without friction or derailing.

I think it worked out just fine, and so despite its size, the steam engine is able to navigate tight corners and busy marshaling yards.


Just like the 7777, this design is equiped with three yellow front lights in the steam engine and 2 red back lights in the tender, illuminated by 3 light bricks.


Most parts used in this design were available in 1980. I made a point of using these very specific (and now very expensive) 7750 bricks, just as the steam engine from 7777 does.

selection of used parts

In the end, this MOC contains 5 or 6 parts that were available only later in the 1980s: 2357, 2431, 3039px6, 32001, 4150, and 4592/4593. If you really want, you can redesign these easily. This MOC really could have been going around your tracks in 1980.


In order to rotate the box, use either 1. the space bar, 2. the numeric keys 0-9, 3. the arrow keys, or 4. use the mouse to rotate (left mouse button) and zoom (mouse wheel) the box. Double-click to open and close the lid. Press Esc to close the viewer..