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.

2 Answers 2


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)

Camshaft sprocket

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

  • Thank you for attaching the image. The image answered my question clearly.
    – ShanjayG
    Commented Nov 18, 2020 at 16:13

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.

  • I'll add that precise timing is also very important, on most engines at least, to prevent damage to the pistons and valves. Today most engines are of the "interference" type where the valves open into the cylinder such that if the piston is at TDC (i.e. its point of maximum travel) that the piston and the valves would interfere. That usually means a bent valve or worse.
    – jwh20
    Commented Nov 18, 2020 at 14:18

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