Knocking Noise After Timing Belt Change

I have a 2005 Standard 2.5 RS wagon - nice little car.

So with that in mind, I had a local garage (trusted…dealership in this area is notoriously crooked) replace my timing belt, tensioner, idlers, thermostat, and water-pump last week. I’ve had the car back for about 3 days and I just noticed today, that while the car is idling, I’m hearing a knocking noise coming from the engine somewhere (could be while I’m driving too, but maybe I just not hearing it) - I don’t recall this sound before bringing it in for the work. When I rev up the engine a bit, it goes away, but when the car sits for a few minutes, it comes back.

I’ve already had it back in since the change for a defective tensioner, which the garage replaced free of charge. I plan on calling them first thing Monday morning to bring it in so they can have a look, but in the meantime, any idea what this likely to be?

Thanks for any help!


Can you explain the whole story with the defective tensioner? What happened with the car that had you notice that problem and bring it back in?

Was all of this work just routine maintenance? Or was there some problem before?

Anything lighting up on the dashboard?

There’s not enough known about this car to make much of a guess at all so I will only pose a theory.
Maybe this knocking noise was actually present before the work was done and was simply not noticed. After work is done many people often start tuning in a little closer and notice things they did not notice before.

I’d be interested in knowing the mileage and oil change regimen in the event this is a subtle rod bearing rap, etc.

Like others say, we need to know more about the recent history. It’s unusual that a tensioner would be defective after the work you had done. That indicates to me the timing belt installation may have not been done correctly, but without more info it is hard to say.

I can’t say what is involved on your car as I’ve never done one on that make, but installing a timing belt on a Toyota Corolla (which I have done) involves removing the front engine mount, loosing the mid-engine mounts, and jacking up the engine and is a fairly invasive procedure. That has to be done very carefully in order not to break something. If an engine mount isn’t put back on correctly or tightly enough, that could cause a noise, especially on acceleration I expect. The timing belt sets the valve timing. It has to be put on exactly as spec’d, the alignment marks have to be aligned correctly simultaneously on the crankshaft and camshaft, otherwise the valve timing will be early or late. Early or late valve timing would likely cause a knocking noise too. There’s a possiblility the new water pump could be faulty too. That could cause a knocking sound.

It’s frustrating, but don’t feel too bad. I recently installed a starter motor and a knocking noise appeared afterward. I’m still working on that one!

The mechanic who did the work said the initial tensioner was leaking oil, and thus not applying the correct tension to the belt, which in turn was making the engine sound as if it was whirring while driving. So I brought it back, he replaced it and all seemed well. However, today I noticed that the car was knocking (almost sounds what I think of as a Model T) when idling. I suppose it could be that I’m hypersensitive to noises now that some work has been done. My car is currently at 99,500 miles and I Subaru recommends that this belt be changed around 100,000 miles, so it was “routine” in that it was manufacturer recommended. Finally, no lights coming on in the dash.

As far as oil changes go, it has had regular oil changes every 3,000 - 3,500 miles. I probably would have had this done at the dealership, but as I indicated in the original post, they are not known for treating their customers very well and generally, when I’ve gone there they find 3 other things that are “critical” or “necessary” and want to charge an arm and a leg to do the work (i.e. PCV valve they wanted $105 dollars to do…I did it for $8 and it took 10-minutes of my time).

I hope that gives enough info. for further discussion.

Thanks for the replies!


If the knock was definitely not there before the timing belt work and it’s there now then this could point to something being amiss. What that would be I have no idea.

A valve lifter can knock if loose enough but these usually come across as a tap rather than a knock and has nothing to do with a timing belt change.
One possible cause of a knock, assuming it was not presente before the work, could be a crank pulley or harmonic balancer that is loose or damaged. It is hoped that this would be caught, especially if they had to go back in on this bad tensioner and hopefully the bad tensioner story is not a tall tale that is being related in an effort to cover up a screwup.

I’m not accusing the shop of any wrong doing here; just pointing out that things like this do occur.

It might be the OP has become hypersensitive to engine noises. I used to own a 1970’s VW Rabbit, which incidentally is why I had to learn to fix my own cars otherwise I’d have been in the poorhouse for sure, and after one fix I started to hear this “whining” noise especially on acceleration. It turns out this noise was always there. It was the fuel injectors whining. I just never paid any att’n to it before.

How can a timing belt tensioner leak oil?

My first timing belt I ever did was on my 72 Vega. When I put the belt on it was knocking very badly. So I opened it up again…and the belt was off ONE TOOTH on the cam. Removed the belt and put it back on (CORRECTLY THIS TIME). And knocking went away.

How can a timing belt tensioner leak oil?

Only thing I know that can leak oil in that area are the cam and crank seals.

Many engines equipped with timing belts use a tensioner that is considered to be a hydraulic unit. These are not operated by engine oil pressure and work, sort of, on the same principle as a shock absorber. It’s possible for a hydraulic tensioner to leak or seize up.

If the noise was in all honesty not present before the work then it could be caused by someone being off a tooth or two on the cam timing and the noise could be due to the intake valve heads lightly tapping the pistons.

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I just had my timing belt and water pump and i believe tensioner changed it was a kit. I got it home no problem and some days later a lose rattling noise is coming from my engine it seems like a lose rod or something bouncing all around its the weirdest noise I have never heard a noise where i cannot identify where or what the problem is and none of my shade mechanics know what it is… The car has been maintained at all intervals it has no leaks so this has to be something the mechanic did possibly not timing it right i would think… I notice he has not called me back or will give me a time to bring it back over so i think he knows what it is but does not want to back up his work. I have to now pay another mechanic to tear the car down and fix what is broke or simply time it right.This engine has a Cam so i hope it can be adjusted and fixed. I will check back in and let you know if this was the last mechanics fault or bad luck.

Maybe you should drive it to the shop that did the timing belt. It’s much harder to ignore someone in the building.