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Four stroke petrol engines

Suck, squeeze, bang, blow. That’s all you need to know!

Four-stroke internal combustion engines work on a four action/stroke process:

  1. First stroke: The piston draws a mixture of air and fuel into the cylinder through inlet valves. In classic engines, this air and fuel mixture would be delivered via a carburettor.
  2. Second stroke: The piston pushes back into the cylinder, pressuring the mixture.
  3. Third stroke: The pressurised air-fuel mixture is ignited by a spark from a spark plug. The timing of this spark it managed by a distributor. The resulting explosion pushes the piston and creates the main driving power of that cylinder.
  4. Fourth stroke: Having spent its energy the piston pushes back, forcing the spent gasses to escape through exhaust valves.

This four stroke system has proven itself to be a very efficient way of transferring the explosive power of the fuel into motion via a crack shaft.

With a common four cylinder engine each stroke can take advantage of one piston providing its explosive and force-generating stroke – meaning constant and smooth power.

As engines have developed the number of cylinders and layouts of those cylinders have varied greatly, from a single cylinder engine through to V-formation 16 cylinder engines (V16).

Engine History for cars and motorcycles

 



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