LEGO Pneumatic Tractor Mk1

So here it is finally!

Over a year ago, I managed to build myself a prototype pneumatic engine out of LEGO, after viewing some examples on the Internet. I was quite chuffed that my initial version worked so well, that I even posted a video about it. Then it seems, nothing happened for a while. Well really, it did, I just neglected to blog about it!! :( So, here it is, the main model which resulted from my dismantling the LEGO Unimog kit I had blogged about a while back.


So what exactly is a pneumatic engine you might ask? Well, a long time ago, Lego came up with the idea of incorporating pneumatic cylinders into their kits. These are basically cylindrical rams powered by low-level compressed air and were designed to operate kits with crane arms and other such creations. It seems however, that Lego builders around the world (me included) will always find ways to re-purpose these parts and thus, the pneumatic engine is born. Looking on the Internet, there are quite a few different types of these engines, some operating at crazy-high, Lego part-melting RPMs. Others (such as mine), operating at more ‘reasonable’ levels of speed, and boasting steam-engine-like levels of torque. In this post I’ll give a ‘teaser-like’ overview of the main points of the tractor, but I do hope that related documentation and assets, such as the video at the end of the post and also the images will be able to do some of the talking too.

Also, be sure to check out the detailed Operator’s Manual which I’ve written for this tractor!! (link at the bottom of this post also)

How the pneumatic engine works

I have, as aforementioned, already written a very in-depth operator’s manual regarding this tractor, and so here’s an excerpt from the manual, which I think describes the principles of the pneumatic engine best:

The engine operates because a flow of compressed air is directed to each of the two cylinders in a predetermined sequence. Once compressed air reaches the inside of the cylinder, it is directed to push against a piston, as it has nowhere else to go. Each piston in a cylinder is connected to the engine’s crankshaft, which is forced to revolve as the pistons move up and down. Finally, the crankshaft is connected to the Tractor’s transmission.
The engine can continue to run as compressed air flow to a given cylinder alternates as the piston in that cylinder moves up and down.

As the piston reaches the bottom of a cylinder, compressed air is routed to the bottom of the cylinder to push the piston upwards.
When the piston reaches the top of the cylinder, the compressed air is routed to the top of the cylinder, pushing the piston down, and the cycle repeats as long as compressed air is supplied.
This is referred to as the ‘double-acting’ or ‘double-action’ process.

The result is a continuous rotation of the engine crankshaft, which is directed to the transmission, which then feeds power to the rear wheels.

Other components and systems

I saw fit to load this tractor with as many systems and components as I could, being that I had quite a lot of parts left-over from the dismantling of the Unimog. So, here’s a short list of the systems and features of this tractor, in addition to the pneumatic engine (I’ll mention the engine again anyway ;)):

  • Two-cylinder double-acting, non-reversible, pneumatic engine – runs on air alone
  • Two-speed forward and one-speed reverse constant mesh gearbox
  • Automatic pneumatic parking brake featuring twin-brake shoe design
  • Drag link steering system
  • Rear differential
  • Rear pneumatic-operated ram (actuates various accessories)

The Operator’s Manual I’ve written describes these systems (and more) in much greater – almost exhaustive – detail. Be sure to check it out (link at the end of this post)!


Here’s some pictures of the tractor as well as a video and a link to the very detailed Operator’s Manual. Enjoy!!

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Link to the Operator’s Manual PDF

Where to now?

So what’s next at the Harman Motor Works? I am currently working on a remote-controlled Lego bus, to be based loosely off an AEC Regal MkIV single-decker. This Lego bus is fitted with my latest prototypical fluid drive coupling, of which I’ve also recently blogged about. I’m currently at a reasonably-advanced level of completion of this vehicle, having got the rolling chassis and box frame mostly complete. There is however still quite of bit of work to go. I will post an update or two on this blog over the coming weeks!

Here’s a sneak-peak at what the Harman Motor Works work-bench looks like at the moment: