I recently had a situation where I needed one (did my brother bend valves when his timing belt slipped because the terrible noise of a seized waterpump under the hood was not a concern to him?...stay tuned to find out), and I got a USB endoscope on amazon for like $18 -- I don't even know the brand, but the ones for like $10 had terrible reviews. Anyway, a coat hanger and some duct tape and I was looking at the top of the piston with my laptop. I was amazed it work as well as it did. Good lighting, etc etc. Could take and save video.
If you're in a situation and you need a cheap peek inside somethin', you can't really beat it.
