Make sure your inside hole for the engine is not flat, and that it has an angle. If it is flat, the printer needs to print supports for it, and that would be in the way so you would not be able to put your engine in.
You can either do this using the hole tool originally and make the angle at the bottom of this picture to the right smaller, or you can use the chamfer tool on the top of your hole to angle it up instead of being flat. |