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Home > Engines > New Project: Plans for a Simple Air Engine

New Project: Plans for a Simple Air Engine

Material: Aluminum, Steel, and Brass
Units: (in)


If you’re looking for a simple engine to build that runs on compressed air, here’s a nice set of plans for you. Here’s what Rob had to say about his plans:

“This was the semester long project we did in class for Machine Tool Technology at the University of Central Missouri . I would like to hook the engine up to something and do tests.

The base is made out of a 3/4 in thick aluminum and the body and cylinder is mild steel. The flywheel and crank is made out of brass. I used most tools that you would use with metals. Vertical mill, horizontal mill, metal lathe, drill press and grinding machine, thread tap. I even machined the threads on the wrist pin.”

- Rob K.

Here’s a video of the little engine in action:

Thanks for sharing your plans Rob!

  Air_Engine.pdf (1.1 MiB, 2,850 downloads)
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About Tyler

Tyler is a hobby machinist and 3D printing aficionado. He teaches computer programming and web development at Highline College near Seattle. Tyler founded Projects In Metal in 2008 because he was frustrated by the lack of free plans available for hobby machinists.


  1. If there's enough weight in the crank web and counterbalance you stand a chance, but I'll stick with my thoughts as the engine is utterly dependant on the flywheel action for most of its rotation. At the very least it'll need speed to overcome this with your lighter flywheel, so it may work at the higher rev ranges.


    I'd love you to prove me wrong though to be honest so that it works for you, as I said I'm not close to that particular engine, so I'll wait to see what prevails.

  2. I will re-post the out-come as soon as time permits me to do so.


    Mtw fdu.



  3. Smaller engines will run fine without much of a flywheel.  However, they will not run at slower speeds, and will require more air pressure.  Since I prefer my engines to just tick over, as opposed to running flat out, I tend towards a slightly oversize flywheel, and usually use brass.  More mass will allow the engine to coast more, and let you run the engines on very low pressures – less than 2 PSI  in most cases.


    With such a small engine, even adding a rim of steel (think galvanized conduit) will help with lower speed performance.  Black iron pipe would also work well. 


    BTW, if there are children in the neighborhood, invite them to look at your engines.  Kids love to watch them run.  I get asked at least a couple of times per year to bring out the ones I have made and run them.

  4. How do you put this engine together?

  5. Looks a lot like a simply air engine from a machining book, we have in metal shop. I might scan them and then start a new thread.

  6. I haven’t built this engine myself, I shared it with permission from the original builder. What part of the assembly are you having trouble with? Have you machined the parts yet? I think as you machine each part you’ll start to get an idea of how everything goes together. But if you’re stuck let me know and I’ll try to help with the assembly.

  7. Ok. Yea thanks. But as you said I think I’ll be able to see it better when I have everything done in metal shop. But If I have questions I will for sure ask.

  8. Sounds good. Happy turning!