Do a Google search for Vividia Ablescope and you'll see an articulating scope that's pretty useful for cylinder inspection. They make a few versions, from rigid to flexible and semi-flexible from $200 to about $400. You'll find a number of videos showing the inspection of valves using the articulating feature.
RV-8, SN-80587, built, flown, sold.
RV-3B, SN-10751, rotary engine, built, flown, sold
RV-8, SN-82470, built, flown, sold.
RV-3B, SN-11351, purchased (yes it's cheating)
A&P - 2018 dues paid