Modular Compressed Air Engine - Ultra simple - Easy print

Here is my 15.1mm bore x 8mm stroke air engine, It has no moving parts other than the piston and crank, it is very simple to build and is modular, so you can make any configuration you like. You only need about 5 files to make a working engine, the rest are supplementary. It can run at very low pressure, once well run in, it can run with you blowing down the inlet and at 5 bar it absolutely screams. There is a video on the youtube page about how to assemble.

It should run without any post processing, it can be easier if you deburr everything and give the pistons a light sand with fine sandpaper. Each STL is already in its optimal print orientation. Print everything at 0.2mm layer height, except the cylinder which is better at 0.1mm.
Hardware required:
8x14x4 ball bearings - these go onto each crankshaft end
5/32" (3.968mm) ball bearing - (I'm certain it would work on 4mm if that's what you have) - This goes into the cylinder head and acts as a valve.


edit 16/12/2025
There is now a "