How to Tell if a Timing Belt Tensioner Is Bad

Co-authored by wikiHow Staff

Last Updated: September 20, 2022 References Approved

Replacing a timing belt is one of those things that scares most car owners because it is an in-depth job and usually quite expensive when done at a shop.^{[1]
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Research source} More often than not, it is actually the tensioner that goes bad, not always the belt (unless it is really old). Most of the time a belt will break due to a seized pulley or bad tensioner allowing it to contact the timing cover.

Steps

1
Listen. A bad tensioner will usually be accompanied by noise.^{[2]
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Research source} This noise could be some type of squealing or rattling coming from the timing cover area. Also, when your timing belt is loose, it will cause some drivability issues usually under high load or high rpm. If your timing belt is not properly tensioned it will not keep the valves timed properly to the lower end and this will cause misfires, loss of power, bucking, and could even cause a no start condition.
2
If the car runs, then stand on the side of the car where the pulleys are and try to distinguish where the noise is coming from. If you hear the noise coming from the front of the engine and it is not coming from your accessories, you may hear the belt flapping around due to the loss of tension.^{[3]
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3
If the car doesn't run and you are going to be the one doing the work, then remove your front accessories enough to get to the front cover. Once done, remove the front cover and check to see how loose the belt is. There should be a little slack on the opposite side of the tensioner, but not much.^{[4]
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4
With the cover off, check for the free movement of all the idler pulleys and the tension itself. It will be very apparent if something is broken.
5
While you are in there, it is smart to just get a timing belt kit and replace all the pulleys and the belt.^{[5]
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6
Make sure that you line up all your marks and set the proper tension on the belt.

Community Q&A

Question

I have had to change my timing belt twice within a year. What could be the cause?

Community Answer

First, check that none of the teeth that the belt is riding on are worn. Worn teeth will dig into the belt and cause premature wear. Then, check each gear's bearing. The belt tensioner bearing is the most likely one to fail first, but it's usually the easiest to check and fix. With the belt off, spin the belt tensioner (which is usually the plain, smooth wheel on a spring loaded arm; the smooth side of the belt rides along it). A bad bearing will not spin as easily and/or will sound rough. Finally, check for rubbing. See if anything is rubbing against the belt, causing it to fail.
Question

How can I know whether the mechanic has been truthful about the timing chain tensioner leaking and it costing $1000?

Fouad Martin Yousfi

Community Answer

The timing chain tensioner is a part that requires a lot of work to change. That's caused by the necessary time to reach the tensioner and to synchronize the chain, which is in the engine, not as a belt that is external. Sometimes, to prevent maintenance, your mechanic can change the chain, as if the tensioner was bad, the chain may have some damage too, and a good mechanic would take a profit of the removal to change everything that may need some further costly maintenance or irreversible damage. As far as the mechanic being truthful about it leaking, you could take it to another mechanic for a second opinion and quote.
Question

Do I always have to get the "kit" for replacing the timing belt, or can I just replace the belt?

Community Answer

The kit is only necessary if you do not have the other parts or tools that it includes. If you have these items, you may replace the belt alone.