Water pump has missing or broken teeth, or sprocket falls off the shaft.
Probable Cause of Failure
Misalignment or damage of the tensioner, guide or chain.
Visual inspection is required to verify the correct alignment of chain tensioner and guide. Inspect for broken, cracked or missing guide material as well. It is not advised to reuse misaligned components. Also, check the chain for any imperfections.
Figure 1: Correct alignment of tensioner and chain guide.
Figure 2: Incorrect alignment of tensioner and chain guide.
Figure 3: If the chain looks like the circled areas, it is time to replace the timing components. Notice how the chain sags; this should not occur in any location of the chain drive. If slack is present, replace the chain, chain tensioner and chain guides.
Figure 4: In these circles, there is no slack present. This is the optimal position for the chain.
Courtesy of Gates