Timing Marks on Engine, Timing Chain - Conceptual Question

[YoshiMoshi]

TL;DR

Why do you need to to line up the timing marks?

On an engine, the timing chain has colored links, and you have to line up these colored links on timing marks on the engine. There's typically marks on sprockets, bearing caps, gears.

A understand that you have to line these up in order to get proper timing. I understand that is the reason why, but conceptually why does not doing so result in the engine not getting properly timed? I do not understand conceptually what is mechanically different, as it's still the same timing chain that is of the length, going around the same sprockets.

 

[jack action]

The timing chain synchronize the rotation of the crankshaft and the camshaft. This synchronisation ensures that the engine's valves open and close at the correct times in relation to the position of the pistons. (source)

 

[Baluncore]

I do not understand conceptually what is mechanically different, as it's still the same timing chain that is of the length, going around the same sprockets.

It is the same chain, or the same timing belt, so the marks on the belt or chain do not have to be correct. So long as the correct number of links, or steps are between the pulley timing marks, it will work. It is easier to get it right the first time if the chain or belt is marked. Marked links reduce the accuracy that the pulleys must be lined up with the engine block or head marks during reassembly.

There will be a factor of two between the crank and the cam. If the length of the belt, in links or steps, does not share prime factors with the crank or cam gear, then the chain or belt will wear evenly once the engine is started. That is the equivalent of a hunting tooth in a gear train.

 

[Lnewqban]

TL;DR Summary: Why do you need to to line up the timing marks?

Please, see this important reason in certain types of engines:

https://en.wikipedia.org/wiki/Interference_engine