A friend showed me this today. Depstech WiFi Endoscope. I don't like the name endoscope but it function very well. LED lights on the end to illuminate what you want to see. Use a smartphone to connect to the scope through WiFi. I found it to be really clear and could get quite close to the subject material. Has a couple of attachments for the end. I can see how it might be useful for cylinder inspection through a spark plug hole.
http://www.depstech.com/?portfolio=depstech-wifi-borescope
http://www.depstech.com/?portfolio=depstech-wifi-borescope