This is a very small air powered engine. It works with a very simple rotating valve mechanism but is not efficient because the seals are not very good. It does however work pretty well.
If you have any questions or suggestions feel free to leave a comment.
You need this hardware:
2x 7mm 2m screws with 3.5x1 mm heads
2x 4mm 2m screws
a small tube with an OD of 4mm
You should enable a brim since the parts are very small. You also should print this with 100% infill so the fly wheel is just a bit heavier. The print time is about 1 hour and 15 minutes and it uses about 6 grams of filament. It can be printed with a standard 0.4mm nozzle. I used pla.
To get it to work you need to sand the inside of the cilinder and the outside of the piston until the piston slides very smoothly inside of the cilinder but is not lose so it maintains a good seal.
You also need to sand the rotating valve pin which is also part of the crankshaft. and the hole the pin goes in. Try to get these to fit perfectly so as little air as possible will be leaking away but the pin has to be very easy to rotate.
Next you need to fix the connecting rod to the piston with a 2m screw with a head of about 3.5mm x 1mm and a length of about 7mm.
Slide the piston into the cilinder and insert the timing valve in the cilinder part aswell. Next screw the crankshaft to the timing valve with a 7mm screw and the connecting rod to the crankshaft with a 4mm screw. Also screw the fly wheel to the timing valve with a 4mm screw. Push the type in the air intake hole.
Finally you should add a bit of lubricant to the moving parts and the piston. Silicone based lubricants should be used for plastics but I just used a bit of petroleum jelly because I didn’t have any. No lube seems to work pretty well too.
Adjusting the timing
You can test it now but it probably won't work because we haven't adjusted the timing yet. you do this by unscrewing the screw that holds the timing valve onto the crankshaft a bit. then change their position and screwing the screw back in. You want the valve to open when the piston is just going down again and closing when it is almost fully pushed down. You can blow some air in the tube to determine when the valve is open.
To make it run attach it to some sort of air supply and give it a push. I adjusted my timing so it would go clockwise so I need to push it clockwise.
I got mine to work at 1 bar of pressure but it worked a lot better at 3 bars. I haven't tried a higher pressure yet.
It is very inefficient because of the leaking valve but it works just fine. I don't think you can power anything significant with it though. Maybe a small propellor?