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Q: Knocking noise. Is it a problem with the belt?

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The higher the rev the faster the knocking. I found that a common problem was a bad timing belt hydraulic tensioner. I was able to remove and re-instal it without removing the usual components and covers . I gained access by only removing the passenger side tire and the two screws that hold the tensioner. There were no apparent leaks but it has an indentention at the end of the piston instead of a rounded end. I took it the a local auto parts store and compared it to a new one. There was a difference in length; about 5 millimeters. Am I correct to assume that I shouldn't have been able to reinstall it if there was tension on the belt? The car runs just fine. No dashboard alarms or check engine lights. Thanks

My car has 137000 miles.
My car has an automatic transmission.

A: Hello - No, it is incorrect to assume that ...

Hello - No, it is incorrect to assume that you couldn’t install the new tensioner even though it is of different length. Was the new tensioner longer or shorter? If shorter, there may not be adequate tension on the belt, and the engine could "jump time", with expensive results, especially when the belt is at the end of its service life and has stretched. Many manufacturers have introduced new tensioners over the years that improve the consistency of tension on the belt. The recommended change interval for the belt is 105K. The belt costs $40 or so, plus installation. The engine costs $4K+. If you have not changed the belt, idler pulley, as well as the tensioner, I highly recommend you do so. A certified professional from YourMechanic can come to your car’s location to perform a timing belt replacement service and any other recommended repairs at your home or office.

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