This is a functional 3D model of a four stroke engine disegned by me in SolidWorks for a school project, later printed and donated to my school for educational purposes. For the assembly i used some wood and M6x1 screws and nuts, as well as an M6 threaded bar for the handle and 2 custom-made springs; i also used 2 pieces of steel wire folder to a ring similar to a seeger, since a didn't dispose of them. The assembly is pretty straight-forward, and the images should help you in the process. If you happen to print it, please share it. 
enjoy :D