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Noticeable knocking after timing belt change

I have a 2005 Toyota Camry with 120K miles that was bought used with 110K. The previous owner did not have the vehicle long and did not know if or when the timing belt had been replaced. I have read several blogs that recommend replacing the timing belt at 60 or 90K. To err on the conservative side I decided just to do it at 120K. Now my problem. Before the timing belt change there was a slight knocking from one of the cylinders. After the belt change the knocking is more pronounced. Q. How concerned should I be that the knocking is more noticeable? Could this be a by-product of the new belt and as it loosens the knocking will subside somewhat? OR, am I looking at valve job or worse?

You should be very concerned. Since you were hearing it before the belt change, don’t assume that the new belt is the cause. It very likely simply caused an existing problem to be more pronounced.

Take this to a reputable independent shop, tell them all the derails you can, and let them diagnose it. I’d be inclined to first want to determine if it’s coming from the top of the engine or the bottom, but let the mechanic do it his way. You have a V6 (I know that because the I4 uses a chain), so diagnosing it will also require determining which bank the knocking is coming from IF it’s coming from the top of the engine.

Possible causes include a damaged crank or rod bearing from oil depletion (the prior owner may have let the engine run dry), so be prepared to make a serious decision.

Post back when you have some information.

Under what conditions does the knocking occur? Also, is it a deep dull knock, a pinging (spark knock)?
Is it constant under all acceleration/deceleration conditions?

Did you do the work? Did you verify timing marks were correct before removing belt? Just wondering.

Just for comparison, I had the timing belt/water pump, etc changed on my 2006 Sienna V6 (3.3L) back in July. There was no difference in engine performance or sound before and after the work was done.

Ed B.

Is this knocking noise present at idle with the vehicle not in motion?

Just wondering if this is valve lash issue or EGR fault although a belt change should not affect the intensity of a knock.

Are you sure the knocking is from one of the cylinders? Was the belt tensioner replaced with the timing belt?

Good posts above. Here’s a couple of other ideas.

After a repair procedure such as this sometimes extra gas can accumulate in the cylinders or intake manifold (due to various things the mechanic might do to effect the job), and that can cause a knocking sound at initial start up. But it will go away after driving, certainly by the first mile.

How do you know the prior knocking was from one of the cylinders? Test this idea by using a mechanics stethoscope (or just a length of garden hose) to pinpoint the source of the sound. It might be some accessory making the noise.

Pre-ignition knocking within the cylinders can occur if the ignition timing is too far advanced. That is a simple thing for a mechanic to check. Some engines use knock sensors, and those can go bad, so that’s another possibility. Carbon build up inside the cylinders can do this too, although unlikely in a Camry with this relatively low miles unless thee has been a prior mixture problem. The check engine light hasn’t been on for a long time, right? Even if the CEL is off and always has been, you’ve had the ECM diagnostic codes read and found nothing, right?

Pre-ignition knock could result if the timing belt notch alignment was off. You manually rotated the engine a few times and verified all the timing marks associated with the timing belt were spot on, right?

I doubt the knocking will resolve itself as the belt ages. Don’t count on that as a solution. The belt material is designed to change as little as possible with use. If it changed, it would cause no end of problems.

When you changed the timing belt, you replaced the tensioner too, and did what the manual says to set the tension, right?

Knocking sounds, usually described as “tapping” sounds, can be caused by valve adjustment problems or lifter problems, if your car uses hydraulic lifters (which I doubt it does). Replacing the timing belt wouldn’t affect that though.

It would have been better to find the source of the knock before doing the timing belt. Did you hear the knock before you bought the car?