A camshaft timing mark is an arrow or a line scribed into the camshaft that aligns with a corresponding mark on the flywheel to indicate the proper position of the shaft. Typically used as a reference point when changing a timing belt, or timing chain.
Failure to properly time the camshaft results in loss of power, which can cause severe engine damage. It is generally recommended to rotate the engine so that the timing marks are in the top dead center position, and locked into place, before removing the timing belt or chain. There are typically several timing marks located at each connection point between the camshaft and the crankshaft. All of these indicators must align properly.