YouTube channel TRODesigns has come up with a custom internal combustion engine based on a 41-year-old Honda XR75 bike engine, outfitting it with a transparent cylinder to provide a glimpse inside the workings of the four-tact unit.
The team took care to produce the cylinder out of see-through acrylic glass and polished its walls to eliminate any excess friction. They also implemented Teflon piston rings for greater durability and efficiency, leaving all other components as they were. The boost pressure was dropped from 9.5:1 to 8.7:1 for better visibility of the combustion process.
An 18-minute long video provides a detailed overview of the engine, the conversion, and its operation (in the beginning and the end of the video). Note how the walls of the cylinder remained transparent even after intense use.