Scraping noise when accelerating

**Blknight.aus** · 14th January 2011, 01:23 PM

actually if thats the case it generally proves you have a harmonics related problem....

so it could be anything that hangs off of the engine or is connected to the chassis

if it was a bearing problem in the engine it would be most noticable at low engine rpm under higher loads like when you take off in first or second gear when the oil delivery pressure and flow is at its lowest. metals that come from crank bearings tend not to just wind up in the filter a lot of them simply fall out of suspension from the oil at the strainer and sit in the bottom of the pan.

I strongly suspect that we're not looking for something thats going to be fatal to the engine more likely something simple like a failed exhaust gasket, something fallen into the valley cover that you cant see, a shield thats weakend or a vac leak. a decent recording of it might reaveal it to be something that someone else has already experienced.

**Rudolf** · 15th January 2011, 06:05 AM

Torque vibration?

Can't download the sound file.

**jiri_j** · 15th January 2011, 06:09 PM

I uploaded two sound files onto the following links:

1. First I tried to accelerate and keep the engine at 2500-3000rpm and then started to brake. As a result of a high load condition, noise starts to pick up. The noise is like metal-to-metal 'worn bearing' noise. I can't hear anything at idle or when cruising, only when accelerating (higher engine load).

http://muj.optol.cz/janousek/LR/LR-D2-noise1.wav

2. The second recording is the same, but at low rpm of around 800-1000rpm. The noise is very obvious rather at the end of the recording (at 44seconds, low frequency rattling-like noise).

http://muj.optol.cz/janousek/LR/LR-D2-noise2.wav

Anyone has an idea what is going on??? Has anyone heard a similar noise? I tried to check everything in the engine bay area and found nothing. I have a very bad feeling that the noise comes from the engine. I ran the engine without the serpentine belt and noise is still there. Noise get worse when the engine is warm. Noise is RPM dependant. I checked engine oil for metalic particles, looks pretty clean, only a very few tiny metalic chips. I didn't try to open the filter though.

A few of you mentioned TV damper. My disco is V8 and to my knowledge there is no TV damper at the crankshaft pulley on V8. Checked the pulley and it looks to me very solid - no side movements. Any thoughts?

Sully · 15th January 2011, 08:40 PM

I've asked this before, but have you checked your manifold is tight on the block and have you checked the flange gaskets on the manifold where it joins to the exhaust pre-cat?

If the manifold to exhaust flange is buggered the car will make a hell of a noise when under load, but sound fine while idling. It will also get louder when warmed up as the exhaust joins expand more with heat.
Everything you're describing sounds similar to the exhaust flange(s) failing.

**Rudolf** · 15th January 2011, 09:06 PM

Sully's correct. Low pitch noise sounds like cylinder puffing past gasket.

Cam or valve system?

**jiri_j** · 15th January 2011, 09:14 PM

G'day Sully, sorry I forgot to reply you on this. Yes, I did checked all the bolts of the exhaust manifolds at both banks, even between the y-pipe and the manifold. I checked for a cracked manifold as well. Also was looking for any sign of carbon, found nothing. My wife was complaining that in the last couple of days I spent more time lying below the disco then her

But when I think about it now, mate, some time ago I have replaced the y-pipe gaskets (the old design, made of the high temperature material only) with new ones. The new design comes as two thin steel plates with the material in-between. In principle, the gasket could explode within the joint between the pipes and the plates could be making that noise. Good point. I will replace them tomorrow, still got the old ones. Thank you and I appreciate your help!

Sully · 15th January 2011, 09:29 PM

Nice one. It's all a process of elimination. I hope this is the problem as it's a relatively easy fix.

Let us know the outcome after replacing the pipes.

**Blknight.aus** · 15th January 2011, 10:16 PM

it sounds like its only on one pot so I strongly suspect that it is the exhaust manifold gasket on one side or the other.

make up a dummy spark plug on a strong aligator clamp and disconnect one cylinders lead at a time connect it to the dummy plug and then connect the dummy plug to a good earth point.

rotate the dummy plug to all 8 pots one at a time till you find the dud pot and then further diagnostics can commence.

**jiri_j** · 17th January 2011, 08:37 AM

Update: changed the y-pipe gaskets, didn't solve the problem. Measured compression in all cylinders, look very good 170+-5 psi all cylinders. Blown head gasket can be excluded. Will try the trick with the dummy spark plug. The idea here is to run engine on 7 cylinders only, and look for an exhaust manifold leak, correct?

Here I have one question: to make sure that there is no fuel dumped through the exhaust (which could burn the cats) should I remove the particular spark plug? Such that all the fuel goes inside the engine bay area, and not through exhaust?

Is it safe to run the engine without one cylinder by the way? Probably for a very quick drive this is fine, correct? Thank you all.

**jiri_j** · 17th January 2011, 04:35 PM

Bad news: checked for an exhaust manifold leak, found nothing!

I have found out that driving the car at idle speed and introducing an engine load (by braking) I can get the same noise at a low frequency. You can actually hear pretty loud banging :-(

I measured the frequency of the noise and it is exactly at half the frequency of the crankshaft. This means camshaft seems to be a problem.
Why camshaft??? I had an engine rebuild 1.5 years ago (45t km), which involved a camshaft replacement. The reason was a cracked timing cover, which allowed an oil pressure drop in the engine. As a result the camshaft was worn out and had to be replaced.

For this reason I put an oil pressure gauge and monitor the engine oil pressure. No problem at all here. So why a worn camshaft???

Or is there anything else that could make noise at half the frequency of crankshaft? worn hydraulic lifters? These were changed as well by the way. Looks to me I am facing a big and expensive job :-( Any thoughts how to test for a worn camshaft further???

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