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05 LGT limited
405 Posts
I've seen similar belt/pulley failures on other cars in the past. It usually happens with absolutly no warning, and is almost always the fault of a bad bearing. Don't blame the installer unless you can prove he did something wrong. While it is neccesary to remove the tensioner assembly, the pulley itself is not touched, only the bolt in the tensioner bracket. It would be nearly impossible to damage this bearing unintentionally.

Looking at the pictures, I can tell you with 95% cetainty that this was a bearing failure, not an installation problem.

The reason the belt is only burned on one side is that when the pulley bearings let go, it allowed the pulley to cock sideways and only rub on part of the belt. The pulley was probably siezed up, and the friction of the belt sliding across it caused the belt to melt.

I've heard of issues with the SOHC belt tensioners having bearing noises when cold... and from the freeze frame data you posted, it seems that the engine was revved hard while it was still cold, (48 degrees F) possibly this could have caused the bearing to start to fail.

Look closely at picture 7. That is the timing belt tensioner in question. It failed because of a bad bearing, not a hydraulic failure... in other words, the pulley failed, NOT the tensioner itself. While there is a right and wrong way to compress this tensioner, it really does not matter in this case, because compressing the tensioner the wrong way would damage the hydraulic portion, and not the pulley. The idler pulley to the left of the crank gear has also failed... which one failed first? Impossible to say, because the amount of heat generated in the belt by one siezed pulley would be enough to destroy all of the idler bearings.

Could the installer have found the bad bearings earlier? Maybe. As I stated earlier, these bearings usually give no warning before they die, and a simple spin test by hand would reveal nothing, because the pulley would be spinning much slower than normal and with a fraction of the normal load.

In my professional opinion, it is probably not the fault of the installer.

I hope this helps.
John I. ASE Master auto mechanic, General Motors Technical Assistance
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