Importance of marking timing marks on timing pulleys or sprockets when replacing camshaft

Question

What is the importance of marking the timing sprocket or chains or belt, or even using the timing lock on the end of the camshaft when replacing the camshaft, when a new camshaft is attached to the camshaft sprocket  the markings wouldn't be valid is it or is there some specific way that a new camshaft can be screwed back to the  timing sprocket.
Ps: its an overhead cam layout.

user60481 · Accepted Answer

A camshaft can only be attacked to the camshaft sprocket in 1 orientation which you can see when you look at the camshaft sprocket. (See below image for an example)

It is important to know the position of the camshaft relative to the crankshaft, so the timing is correct.

Solar Mike · Answer

Most (all) engines will have timing marks and usually manufacturers provide locking mechanisms or simple holes on the pulley that locate to a hole so a dowel or pin csn be used to locate the position precisely. This applies to crank and cam pulleys.
On some engines, the crank is located by a dowel or pin then the cam is positioned using a dial gauge - once in the correct position then the chain or belt can be fitted. Some pulleys have a method of fine adjustment.
And yes, precise timing is important both for performance and emissions. Had a diesel once that smoked a lot - altered the timing of the cam by 0.5 of a degree and it was much better.

Importance of marking timing marks on timing pulleys or sprockets when replacing camshaft

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