A model of a internal combustion 
2 Cylinder Boxer Engine as used in a Subaru but with 2 cylinders.
No assembly required. 57mm x 20mm.

I found a neat fidget spinner that claimed to be a Boxer …
 but it had horizontally opposed pistons in sync.

→>>- Opposed motion →>>  = (Right + Right) = Out of Balance
->>>- Boxer motion -<<←       = (Right - Left) = Balanced

I based it on the photo of a Subaru crankshaft.

I found many “accurate” models of car engines. But either they were too complicated for a beginner to assemble, then once done  . . . 
 all of the workings were inside the engine and you can't see how it works.

My model just shows the basic internal combustion motion of -
pistons in cylinders, with connecting rods and crankshaft.

[https://imgur.com/gallery/3d-printed-subaru-engine-B0UPvjI](https://imgur.com/gallery/3d-printed-subaru-engine-B0UPvjI)

Engineering:
5mm crankshaft, wrist pins w/ 6mm bearing hole.
Crank offset + - 5mm = 10mm piston travel.
20mm piston, 22mm cylinder.

Designed with Onshape.
[https://cad.onshape.com/documents/c5d9b1fc3176af56a7204183/w/172f515e3efc9db6fe037abe/e/ffd3d4c541a493d21fd628fd?renderMode=0&uiState=68082810286cdf6e72013b46](https://cad.onshape.com/documents/c5d9b1fc3176af56a7204183/w/172f515e3efc9db6fe037abe/e/ffd3d4c541a493d21fd628fd?renderMode=0&uiState=68082810286cdf6e72013b46)