A 4 stroke Gasoline engine.
This is my submission for the weekly 3D print challenge so press like. It will look good on my office desk.
The intake valve is automatic and opens by the vacuum created by the piston. The exhaust valve is operated by camshaft.
The plans were found online but I neded to make some major changes.
If you want to animate the engine (Inventor users only) then expand the crakshaft part in the model tree and drive the supressed angle constraint. Be sure to check drive adaptability. This way the valve springs contract.
I have included STL for each part, 2d plans and 3d dwg file.
The intake tube is roughly designed. I didn't do any calculations for the venturi tube.