Back when I was in High School, I took this class where the final grade was decided by whether or not our 1 Hp motor would turn over, and run for 90 seconds.
We'd be given a 1-piston engine from the school, and we had to take it all apart and put it back together again - every piece.
It was actually quite a rush when mine worked - that was cool.
I've always wanted to take a wrench to my Jeep. I think of things to do with it, but I never actually take anything apart...for the fear of not being able to put it back together again in time to go to work on Monday.
So I'm thinking of getting an old beater, take it apart just to see what makes it tick, and the worst case is I have to get a tow truck to come pick it up and take it off to the dump. All for entertainment.
Now I just need to find a cheap old beat up car.