4 stroke engine has visible inlet and outlet valves on top of the cylinder while the 2 stroke doesn't has them as the piston itself closes and opens valves.

In four stroke there will be a exhaust valve...while in two stroke it is not required

In two stroke engines the sound will be:...dup...dup...dup...dup....dup... in 4 stroke engines the sound will be : drrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr

A 4 stroke engine usually has a distributor that supplies a spark to the cylinder only when its piston is near TDC on the compression stroke, ie. one spark every two turns of the crank shaft. Some 4 stroke engines do away with the distributor and make sparks every turn of the crank. This means a spark happens in a cylinder that just has burnt gasses in it. This just means the sparkplug wears out faster. visit for detail : http://www.deepscience.com/articles/engines.html

In reality a 2-s engine having 1 working stroke after 1 revolution of crank. IN 4-s engine is having 1 working stroke after 2 revolution of crank shaft. 2-s engines are abslute these days. but a 2-s hav a more power than a 4-s. But 2-s engines are not fuel efficient as compair with 4-s engine.