At several of the schools I've attended, they have had engines with see-through cylinders, made of either tempered glass or quartz. I've used a delay-flash timing light, and watched the rings rotate. Perfect Circle Piston Ring Co. had a 216 stovebolt engine in their school several years ago (mid-50's) with a couple of glass cylinders installed. Really interesting to watch the flame travel, and color change while tinkering with mixture and timing!
Jerry
