Cracked Valve Guides

[avguy]

Thanks for posting your findings. It appears that some of these timing belt failures will continue to remain a mystery.

[06T200]

I think the tensioners can fail if the belt is not correctly tensioned. Apparently if the tension is too loose/tight it will allow the tensioner to hit the travel stops, and per the note in the gates kit this can lead to problems. In time they can snap off, and result in tensioner problems. Sounds like the same symptoms anyway.

[avguy]

I definitely agree that too tight or too loose is the cause of some of these failures, and not tightening the WP bolts enough would be another culprit for some of them as well. But also lurking in the shadows, is the group of premature timing belt-related failures with the 2004. It was apparently happening so frequently that Chevy ran a brief program of swapping out the belt N/C for '04 Aveos with less than 60K miles, trying to find out what was causing the early failures. I've never seen an "official" report of Chevy's findings from a reliable source - just some random postings about "pulley failures". So this always makes me wonder if yet another time bomb is lurking in the parts bins. But I still suspect the failures are mainly installation mistakes, and it would be nice if that theory could be somehow shown to be correct, even though that's highly unlikely to ever happen.