First of all i have a video about this project on my youtube channel. I think you should assemble it by watching the video. Watch from here: https://www.youtube.com/watch?v=klcB5OxXbkESTL File: https://www.thingiverse.com/thing:4647106 I designed a 2 stroke engine model in this project. It can be almost completely printed with a 3d printer. You don't need any extra parts. (just bearings)Piston diameter 25 mm and stroke 25 mm. Thus, it has a cylinder volume of 12.25 cc. The bearings I use are 608zz type and have 8 mm inner diameter. (From those used in standard stress wheels).Some parts have 2 versions. One is in full section and the other is in half section. I have added two versions, you can print the way you want.If you have any problems please leave a comment!