UPDATED FILE: New updated file has better tolerances (no sanding) and has modified intake and exhaust ports. 

Toy Engine - Free 3D Print Model - MakerWorld This is functioning engine assembly complete with crankcase, crankshaft, connecting rod and piston. Easy print, looks awesome and super fun to fiddle with and turn. (This model is more meant as a toy than an accurate representation of a 2 stroke motor)

Assembly instructions:

To assemble, start by inserting the piston into the crankcase. Next insert the crankshaft ensuring that the end with the rectangle is facing down. Then proceed to push the connecting rod onto the other end of the crankshaft (it will be quite tight and may require sandpapering for best results) and align the skinny end of the connecting rod with the holes in the piston. Then push the pin into the holes in the piston to secure the connecting rod to the piston. And the most important step; have fun with the engine assembly!