What is a primary difference between a two-cycle engine and a four-cycle engine?

A primary difference between a two-cycle engine and a four-cycle engine is that a two-cycle engine fires every revolution of the crankshaft. In a two-cycle engine, the cycle of compression and combustion occurs in just two strokes of the piston, meaning that there is one power stroke produced for every complete revolution of the crankshaft. This design allows for a more compact engine and contributes to a higher power-to-weight ratio compared to a four-cycle engine.

In contrast, a four-cycle engine completes its power stroke every two revolutions of the crankshaft, as it goes through four distinct stages: intake, compression, power, and exhaust. This longer cycle results in a different performance characteristic, including a lower power-to-weight ratio compared to two-cycle engines when volume and weight are considered. Additionally, the two-cycle engine tends to be lighter and simpler due to having fewer components, but it is important to note that this simplicity can lead to higher emissions and reduced fuel efficiency compared to four-cycle engines, which are designed to operate more efficiently with a more complex structure.