I found these simple GIF images fascinating to explain how engines work and all sorts of other things like sewings machines:

http://mytechnologyworld9.blogspot.com/2010/08/complicated-mechanisms-explained-in.html

crikey, i didnt think a sewin machine was so complicated

crikey, i didnt think a sewin machine was so complicated

Try working out how a sewing machine operator works ( hint -they're usually female ,chattering away about nothing in particular but thinking about larger things than sewing needles) Could it be the action of the needle going up and down - PASS

That's awesome! Is it just me who finds the movement of the radial engine diagram a bit sexual?