Why Two-Stroke Engines Became A Thing Of The Past

As previously stated, internal combustion engines convert air and fuel into energy via, well, combustion, which essentially powers whatever the engine is attached to. Currently, internal combustion engines that use gasoline are divided into two-stroke and four-stroke engines. While their underlying mechanics are the same, factors such as mechanical complexity determine whether an engine is a two-stroke or not.

Internal combustion engines rely on a piston and a crankshaft. Whenever combustion occurs, the piston is pushed down, which rotates a crankshaft. The piston then rises, rotating the crankshaft even more. This process repeats ad nauseam so long as the engine is on. Since the crankshaft’s rotation moves other crucial components, this process powers vehicles and other devices that house the engine, but it is also the main difference between two-stroke and four-stroke engines.

Every time a piston moves up or down — that is considered a “stroke.” In four-stroke engines, the spark plug, which produces the zap of electricity that combusts the fuel/air combo, fires every four strokes (i.e., every other full crankshaft rotation). Meanwhile, in two-stroke engines, spark plugs fire every two piston strokes (i.e., every full crankshaft rotation). Moreover, two-stroke engines are smaller and lighter than four-stroke engines, lack the valves of other engines, and provide more power output for engines of their size.

In four-stroke engines, the air and fuel mixture only takes up the area of the cylinder above the piston, while in two-stroke engines, the mixture is present above and below the piston. Thanks to these factors, two-stroke engines are easier and cheaper to manufacture, which sounds like an advantage. However, these design elements were the main reasons why many modern countries and industries phased out two-stroke engines.