There's a newer version of the engine, that doesn't require bolts. Updated it recently, so there's a higher chance that it will run.
[https://makerworld.com/models/1783606-air-balloon-radial-piston-engine-v2](https://makerworld.com/models/1783606-air-balloon-radial-piston-engine-v2)

Extra parts needed:

• M3x8 Bolts (x15)
• M3 Nuts (x15)
• Nitrile Gloves (thumbs from M sized gloves worked the best)
  or Silicon (worse) or PET (not tested) ones
   

If you don't have M3 bolts and nuts at hand, there's another version of the motor - requires only a glove.

Run by just blowing air into it. Demonstration:
[https://www.youtube.com/watch?v=_FDZzKAFSz4](https://www.youtube.com/watch?v=_FDZzKAFSz4)

Exploded view in 3d viewer:
[https://skfb.ly/6LQBR](https://skfb.ly/6LQBR)

If you like how it works, you can support me by purchasing the Pneumobile chassis:
[https://cults3d.com/en/3d-model/game/pneumobile-pneumatic-toy-car](https://cults3d.com/en/3d-model/game/pneumobile-pneumatic-toy-car) (3d Viewer: [https://skfb.ly/6LV6D](https://skfb.ly/6LV6D))

Works with this remote:
[https://www.thingiverse.com/thing:3675568](https://www.thingiverse.com/thing:3675568)
Or with simpler remote from the Vapemobile set:
[https://www.thingiverse.com/thing:3606204](https://www.thingiverse.com/thing:3606204)
 

Optional parts:

• M3x12 or longer bolts (2x)(for the gears)
• M3 Nuts (x2)(for the gears)
• 6x4mm Silicon Pipe (can be found in aquarium shops)
• M5x10mm Washers (x2) (instead of printed ones)
• 105ZZ Bearings (x2) (noticed no difference in performance)

Printed well with 0.6 nozzle at 0.2 layer height. After printing cut away the brims from Cylinder_Ring parts.

Parts with "X_" in their names are optional.

Assembly:

• Use 3d diagram as a guide: [https://skfb.ly/6LQBR](https://skfb.ly/6LQBR)
• Cut off a glove finger tip (thumbs from M sized glove worked well)
• Pull it onto a Cylinder_Ring (Use Helper_Finger to leave enough height)
• Connect a Piston to it with two Washers
• Clamp the Cylinder_Ring between Cylinder_Plate and and Cylinder_Lid
• Clip them with Helper_Clamp so they won't fall apart at once
• Bolt them together to Plate_Top
• Repeat for the other 2 cylinders
• Insert th Crank with 2 Washers
• Fix it in place with Frame_Bottom
• Bolt all the parts together
• Put the Valve_Inner in place
• Bolt the Valve_Lid into place
• The engine should be running!

Troubleshooting:

1. Rotated freely by hand, but struggling when working - the inner valve may have too much friction against the frame (sanding the valve and the frame may help for a while).
2. Jams on a certain cylinder - this glove finger may need a bit more slack.