What are timing chain marks?

Timing chain marks are indicators that show when an automobile engine is in alignment with the timing chain and cam sprocket. These marks are necessary in the removal and replacement of the timing chain.

When timing chain marks align with cam sprocket marks, the engine is at top dead center. An engine must be at this position before removing the timing chain and cam sprocket.

Reinstallation of the timing chain and cam sprocket requires realignment of the marks. The marks must also be in alignment with the camshaft and crankshaft guide pins, and the engine must still be at top dead center.