I stumbled over these Inspection cameras on Amazon when looking for something else. There are multiple styles, costs and brands of these, but it appears most of them get really positive reviews. At 9mm, can you imagine sticking it down your spark plug hole (with 6 led lights) to look about for issues? I know you can just drop the exhaust pipe for a pretty good look, but you still can't easily see light piston smearing on either side of the exhaust.
I'm thinking I'll get one just in case I need one?
https://www.amazon.com/Endoscope-Inspec ... eld+tablet