Imagine a hollow cylindrical chamber box with another solid box slightly smaller and 10 times shorter inside, which can move length ways within the larger of the two but with enough friction to maintain a seal.

For explanation purposes we'll call the big box A and small box B

This is the fun part;
Now imagine opening A and squirting a mixture of atomised petrol/air mixture whilst pulling down B to induce the fuel. Seal off A with the volatile mixture. This is Known as the induction stroke

Force B up compressing the mixture, at the end of B's travel this is the compression stroke

At this point an electrical spark lights up the mix.....................BANG !

The force of the explosion pushes B back down cylinder A, this is called the power stroke

To perform this task again A must first open with B climbing back up to expel exhaust burnt fuel
Finally this forth action is the exhaust stroke.
This is known as a four stroke cycle and constitutes 4 engine revolutions, this operation is carried out in Milli-seconds.

Ok thats the basic function in simple terms, the mechanics of the engine harness this power in many different design layouts. e.g. Straights, flats, v's and rotaries

Generally four cylinder motors are the most common depending on the application, they operate on the principle that each cylinder fires individually so as to ensure a constant steady output of power in a linked balanced cycle. So as one cylinder fires another is on a compression stroke ready to fire on the engines next rotation.

Continuing on in a mechanical description imagine again A as the larger stationary cylinder and B the movable.

B is joined to a offset shaft by a linkage. The linkage is like a hand gripping a knob handle on a window winder, ie. its rotating the crank and is linked to it yet freewheeling at the same time. This crankshaft is what transmits the power into turning effort.

A is not alone it too has a shaft nearby which is in charge of a set of valves which open and close A to let fuel/air in and burnt fumes out, on the principle of an eccentric cam lobe. The row of offset egg shaped lugs individually appear as the shaft turns to push down on the valves forcing them to open, they are spring loaded and return automatically as the lobe disappears momentarily over the horizon as it were.

The igniting side of the engine is called a distributor, mounted to the camshaft, put simply like an electronic clock which throws an injection of electricity to the spark plug in time with the end of the compression stroke.

These shafts are linked by either chains gears or belts so as to time with one another in a symphony of precision so the four strokes of each cylinder carry out their suck,squeeze,bang,blow cycle.

All other devices and mechanisms perform the tasks of mixing fuel/air, cooling and lubrication by way of mechanically gear, belt, chain, driven and or electrically powered means.

So to summarize the internal combustion engine sucks in fuel and air compresses it then ignites the mix. Transferring the explosive energy into turning effort and on its final stroke it expels the unwanted burnt fumes in order to start the four stroke cycle again.

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