t’s no easy task getting a peek at an engine’s combustion process. Iron and aluminum aren’t transparent, but plexiglass is, making it the perfect material to replace a cylinder head. That’s exactly what the Garage 54 YouTube team did in its latest video, where it took a rebuilt Moskvitch engine, removed the iron cylinder head, and replaced it with a clear plastic one.

The piece of plexiglass was thick and nearly the same size as the engine’s original cylinder head, which made it fairly easy to fabricate. The clear material, which had four combustion chambers carved out and sanded smooth, gave an unobstructed view to the cylinders and valves.

The engine starts immediately without any issue, showing the intricate four-stroke engine process. It’s easy to see the intake, compression, combustion, and exhaust stroke – and it’s mesmerising in slow-motion. The plexiglass provides such a clear view that it’s easy to see the fourth cylinder misfiring.

The plexiglass isn’t as strong or durable as iron, and imperfections are noticeable almost immediately. The video shows the high heat in the combustion chamber warming up the plexiglass and causing bubbles and other imperfections to form. After a bit of operation, the engine also begins to show signs of contaminants and residue collecting.

It runs several times without an issue, though it eventually stops working. It’s not clear why, though a lack of compression is the suspected culprit. The heat generated from the combustion process is likely deforming the plexiglass, which could be letting in outside air. At one point, fuel is poured right into the carburettor, but it floods the engine, which you can watch happen. 

Garage 54 consistently publishes fun content that pushes engineering and cars to their limits and beyond. Seeing the combustion process in action is quite a sight to see.