If you are one of the lucky ones to own a 3D Printer then this STL (STereoLithography) file template might be worth looking at as a toy model of a Toyota 4 Cylinder Engine.

Completely print a fully rotating model. Working crank, pistons, and valve train. The valves open and close!!!. It may not be the most exciting engine but its the only one I had in my garage. Great if you want to learn about engines and how the moving parts in them work. All parts are printed except for a few bearings and fasteners.
More than 3 days of total print time.
The block alone was 34 hours. So make sure you have a well calibrated and reliable printer.

Some print times calculated in Cura at .2mm layer height
Engine Block – 40 hours
Head – 23 hours
Valve Cover – 10 hours
Oil pan – 14 hours

Credits to EricThePoolBoy

Check out this cool video:

Click here for more 3D print templates in STL format.