You can buy a decent little video borescope from Milwaukee at Home Depot ... I use mine all the time .. about $200.
Recently I was able to look into the lifter oil feed holes to see if the oil gallery was clean ... it wouldn't fit into the holes, but got close enough I could see what I wanted to see. Also has built in light at the end.
Every shop should have one. The units with the small camera head, like the Milwaukee will fit into a spark plug hole no problem, around 7mm diameter camera head.
They take some getting used to and only focus on things well within a couple of inches or so, not like you are going to put it into King Tut's chamber and see the whole room
