Intermittent Knocking; How To Troubleshoot?

[Bovien 6]

I have an intermittent knocking noise. It seems to be coming from internally in the engine and follows the revs. If I turn of the engine (even while driving) and restart, it dissappears. The sound is quite loud and noticable up to 60 or so where it gets filtered out by road noise.

 

I heard it once, shortly after the engine (that had stood still for 3 years) was installed. Then nothing for several weeks. Now it shoes itself at almost every 10+ miles drive, after I have replaced cam and sump gaskets. I would think it was related to that, if it wasn't because it did it once before. When I got the engine, the cam best had just been changed though, so it *could* be something in there. But why intermittent?

[welshpug 1,627]

get a video up?

[Bovien 6]

Thanks again. Will do asap :-)

[Bovien 6]

ok, here is a video. Først two thirds of it is with the noise. Than I turned the engine off and on again (nothing else) and then you can easily hear that the very sharp, protruding noise has gone. The noise seems to come from center/right part of engine, possibly up to around valves but impossible to tell for sure.

 

http://dl.dropbox.co...ngine_noise.avi (6,5 MB)

 

It seems of happen every time i'm coming off the motorway and into the city. If its the constant (roughly 3k) revs or heat I can't tell, but it seems to be certain that a few minutes after the motorway, the noise comes and builts to what you hear on the video over a minute or two. Turning off the engine helps every time. When it has been there, I seem to be able to catch a hint of it even after turning off/on compared to if it hasn't shown itself, but that could just be me being overly focused.

 

As mentioned above, it started making this noise after having changed the cam seal (removing both cam cover and timing cover/left cam bearing/clamp) as well as changing seals on the sump and spacer.

During this excersise we also lifted the left hand side of the engine for acces and therefor removing the left and the bottom engine mounts.

Edited November 19, 2012 by Bovien

[Vili 17]

Sounds bit like leaking exhaustmanifold-downpipe seal.

[Bovien 6]

Really? You mean between the manifold and the exhaust pipe? On servicebox I only see a seal between engine and manifold.

 

- It just sound internally to me.. But i can see if I can finde something to push the exhaust a bit with from down under, the next time. That would do it, if the manifold should be the culprit, right?

[Bovien 6]

I'm fairly sure it is not coming from the manifold. Looking down there when the noise is there, it surely sounds like it is an internal sound from or relating to the rotating mass. I tried to put some weight on the exhaust manifold with a stick to make sure, but no change in sound. Also, the manifold felt very stable, not as I would expect it it should be making sound from movement.

 

So.. Any other ideas without having to take the engine apart?

[lemmingzappa 75 1 Cars]

Don't fully rule out the manifold yet as the cracks can be hairline and not easy to spot!

[Vili 17]

Really? You mean between the manifold and the exhaust pipe? On servicebox I only see a seal between engine and manifold.

 

- It just sound internally to me.. But i can see if I can finde something to push the exhaust a bit with from down under, the next time. That would do it, if the manifold should be the culprit, right?

 

There is a donut shape gasket that looks like wire wool between manifold and exhaust. It has a tendency to leak. An also I've never seen GTI manifold that isn't cracked.

[Bovien 6]

There is a donut shape gasket that looks like wire wool between manifold and exhaust. It has a tendency to leak. An also I've never seen GTI manifold that isn't cracked.

 

And this could give the sound in the video? When listening under the car, it defo sound like its not coming down there.

But it is an easy fix, so if you are right, its just a matter of changing the gasket? Just so I understand you. Or are you talking about needing to change the manifold? I might have one available as a matter of fact.