2) Compression stroke - Intake valve closes. Piston moves up to compress the mixture causing min. volume and then the Spark plug fires.
3) Combustion stroke - Ignition of the mixture causes combustion forcing the piston down and back to max volume.
4) Exhaust stroke - Exhaust valve opens and the exhaust gases flow from the engine while min. volume is regained.
There is also fuel injection engines where the right amount of petrol is injected straight into the intake valve (port fuel injection) or directly into the cylinder (direct fuel injection.)
Exhaust sytem - Includes exhaust pipe and muffler whcih muffles the sound of all the mini-eplosions in your engine.
Valve Train - Consists of valves and a rod that has lobes on it, which opens and closes them at the right time. Modern engines have a overhead camshaft arrangement. This means that the camshaft rod is located above the valves rather than below as in older cars. Now you may see DOHC in a car's specification this means that there is a dual overhead camshaft. The reason for this is that high performance cars have four valves per cylinder. Two for intake and two for exhaust. Thus need two cam shafts to feed them. A timing belt links the crankshaft to the camshaft to pefectly time the valves. with the engine.