Both 2-stroke and 4-stroke engines are internal combustion engines, meaning they use the burning of fuel to create energy. The key difference lies in how many piston strokes are needed to complete a combustion cycle.

4-Stroke Engine

• A 4-stroke engine completes a combustion cycle in four strokes or two complete rotations of the crankshaft.

• Each stroke performs a specific function:

  • Intake: The piston moves down, sucking in a mix of air and fuel through an intake valve.

  • Compression: The piston moves up, compressing the air-fuel mixture.

  • Power: The spark plug ignites the compressed mixture, forcing the piston down and creating power.

  • Exhaust: The piston moves up again, pushing out the burnt gases through an exhaust valve.

• 4-stroke engines are generally:

  • More complex with valves for intake and exhaust.

  • Heavier due to more parts.

  • More fuel-efficient and cleaner burning.

  • Less powerful per engine size (due to fewer power strokes per revolution).

  • Quieter due to separate intake and exhaust cycles.

• You'll typically find 4-stroke engines in cars, larger motorcycles, lawnmowers, and generators.

  
  

2-Stroke Engine

• A 2-stroke engine accomplishes the same combustion process in just two strokes or one complete rotation of the crankshaft.

• The strokes combine functions:

  • Intake and Compression: As the piston moves up, it creates a vacuum that draws in a fresh air-fuel mixture through a transfer port. At the same time, it compresses the existing fuel-air mixture in the upper part of the cylinder.

  • Power and Exhaust: The piston continues up, uncovering an exhaust port, allowing burnt gases to escape. Then, the transfer port releases the fresh air-fuel mixture, pushing the remaining exhaust out and filling the cylinder. The spark plug ignites the mixture, creating power on the downward stroke.

• 2-stroke engines are generally:

  • Simpler with fewer moving parts.

  • Lighter and more compact.

  • Less fuel-efficient and produces more emissions due to some unburnt fuel mixing with exhaust.

  • More powerful for their size due to more frequent power strokes.

  • Louder due to combined intake and exhaust functions.

• You'll typically find 2-stroke engines in smaller applications like chainsaws, weed whackers, scooters, and some outboard motors.