This is cool keychain for all the motor enthusiasts out there.

PRINT SETTINGS:

All parts can be printed with out supports. I recommend printing the conrods with 0.12 layer height.

ASSEMBLY:

Join the two parts of the connecting rod and thread a piece of filament through the holes. Then, apply some glue at the joint to secure it completely. Once that's done, align the connecting rod with the holes in the piston and insert the pin. It may take some effort to fit it in as it is designed to be a tight fit, but a couple of taps should make it fit snugly. (I recommend adding a bit of glue to the ends of the pin to ensure it won't come loose).