What happens during the exhaust stroke in a four-stroke engine?

During the exhaust stroke in a four-stroke engine, the primary action that occurs is the expulsion of exhaust gases from the cylinder. After the combustion process in the preceding power stroke, the piston moves from the bottom of its travel back up toward the top of the cylinder. As it rises, it forces the spent gases—resulting from the combustion of the air and fuel mixture—out through the open exhaust valve. This process is crucial for clearing the cylinder of exhaust, thus making room for a fresh air/fuel mixture to enter in the next intake stroke.

By effectively removing the spent gases, the exhaust stroke plays a vital role in maintaining engine efficiency, performance, and overall functionality. It ensures that the engine runs smoothly and prepares it for the next cycle of intake, compression, and combustion.