When I was taking auto shop in high school, I have a hard time visualizing how the engine works as a whole. I finally figured it out after I built something like this transparent model engine from Revell.
I found certain Lego Technics sets to be extremely educational in teaching how gears, worm screws, and pulleys work together to create motions that seem extremely complex. A few years ago, I finally learned how the old Chinese legendary “south-pointing chariot” works after I built one using Lego gears I saved from an old Mindstorms set. I also designed and built an elevator pulling mechanism when I moved to my two-story house. My next project is to build a differential gear so I can understand how it works (see below for instructions).
Lego Technic parts are very precisely made so they lock very well and they can be taken apart and re-used indefinitely. So a comprehensive set of gears can get you to build many things. You can get more gears by hunting them on eBay or salvaging them from unwanted Lego Technic sets. The quickest way may be to get the Lego Education Simple and Powered Machines Set
Here are some materials about using Legos to teach mechanical design:
– The Art of LEGO Design
– Lego Gear Combinations
– Building geartrains and other systems with Legos
– Lego Technic Ideas Book
– Lego Crazy Action Contraptions
– The Unofficial Lego Technic Builder’s Guide
– The Chinese South-pointing Chariot –– a technology from 4,500 years ago
– A Lego catapult and another one with instructions
– Workings of Differential Gear