Engine speed related rattles

dgbalfour · May 4th, 2006, 13:37

I've got a nasty rattle from my 1991 240 SE that nobody seems to be able to cure. I know diagnosing sounds over the internet never really works, but hopefully somebody may have had a similar experience.

It is a metallic rattle that occurs between 2000 and 2500 rpm. It occurs both when the car is moving and when it isn't. Depressing the clutch has no effect on it either. It only starts when the car gets warm (about 2 mins after setting off). Interestingly, if you shut the engine off even after a long run, it won't start rattling again for about 2 mins (this makes it very hard to demonstrate to garages!).

I have tried removing the hot air gatherer from the exhaust with no change. I now think the noise is forward of the cat. A suggestion once was that the manifold to cat pipe is double walled and was rattling inside - inserting screws into this pipe to clamp the two bits together didn't help either.

I've had three independent people try and trace it with no success. My (excellent) mechanic at home found a loose exhaust clamp and tightened this up. That changed the note slightly, but the rattle was still there.

Oh, and it's now been doing this for ~8,000 miles and nothings fallen off yet (which was my original hope in diagnosing it!).

Anybody have any ideas or things I could try?

David

Peter D · May 4th, 2006, 14:43

This could well be the cat itself and may not be doing it any good. Many cats are twin walled with a small gap to allow the inner to run at high temperature but I would have thought that running the engine whilst up on ramps allowing the Mech to listen would have identified this. Rest a screw driver on the cat casing and listen. The twin down pipe has a bracket welded to if which is attached to the gearbox, check this carefully as I have seen these corrode through and one of the pipe rattles in the bracket. You have checked the heat sheild I assume from both ends. I would also read your ECU Fuel and Ignition ( 2 and 6 ) for any fault codes just in case the knock sensor has died. Regards Peter

Clifford Pope · May 4th, 2006, 16:42

Have you eliminated the alternator and water pump from the possibilities?
(Try removing the belts)

Is it purely engine speed related, or does it depend on how hard it is pulling?

ALLOA · May 4th, 2006, 16:43

David, I had a metallic rattle on the Torslanda that frustrated the hell out of me. Eventually I found it to be an insulation cover on the double pipe section of the exhaust prior to it running into the single length (between lamda probe and manifold). This appeared to have become brittle with heat and age and had separated from the spot welds. The cover was paper thin when I removed it. If this proves to be the problem with yours be careful ad there is a fine, flaky insulation material beneath. You probably don't want to breath any of it in!

Clifford Pope · May 4th, 2006, 16:43

Or the timing belt tensioner idler pulley?

dgbalfour · May 5th, 2006, 23:21

Thanks for all your input, it's much appreciated.

I would like to eliminate the alternator and water pump from the equation but I just don't dare run the engine without the belts for that long. Once you've shut it down for a couple of minutes to remove the belts it will need another couple of minutes running again to even consider rattling at you. It's very frustrating.

However, the sound does appear to be close to the bulkhead from down low, around the bellhousing area. I will have another good look at the clamp that Peter mentioned and this insulation cover that I haven't found yet. There are no fault codes being recorded (yet).

I'll be back with news when there is some...

David

Clifford Pope · May 6th, 2006, 07:38

Could it be the clutch release bearing or operating lever loose? You can access that by pulling back the rubber boot.

Peter D · May 6th, 2006, 08:54

Good point Clifford but I would hope thathe has tried appying clutch pressure when he has the noise and the termal response time of the clutch assembly would be more then 2 mins but worth investigation. Regards Peter

Les, slight limp · May 13th, 2006, 21:38

I had a rattle that drove me mad, turns out a bolt had dropped onto the exhaust where the twin section is, used to rattle but only at a certain revs, have a quick look for a foreign object sitting on the exhaust below the geabox exhaust bracket, you never know.

May 14th, 2006, 17:52

It could be the air con pump too

Charlotte

May 4th, 2006, 13:37	#1
dgbalfour VOC Member Last Online: Today 07:56 Join Date: Jan 2006 Location: Bedford	Engine speed related rattles I've got a nasty rattle from my 1991 240 SE that nobody seems to be able to cure. I know diagnosing sounds over the internet never really works, but hopefully somebody may have had a similar experience. It is a metallic rattle that occurs between 2000 and 2500 rpm. It occurs both when the car is moving and when it isn't. Depressing the clutch has no effect on it either. It only starts when the car gets warm (about 2 mins after setting off). Interestingly, if you shut the engine off even after a long run, it won't start rattling again for about 2 mins (this makes it very hard to demonstrate to garages!). I have tried removing the hot air gatherer from the exhaust with no change. I now think the noise is forward of the cat. A suggestion once was that the manifold to cat pipe is double walled and was rattling inside - inserting screws into this pipe to clamp the two bits together didn't help either. I've had three independent people try and trace it with no success. My (excellent) mechanic at home found a loose exhaust clamp and tightened this up. That changed the note slightly, but the rattle was still there. Oh, and it's now been doing this for ~8,000 miles and nothings fallen off yet (which was my original hope in diagnosing it!). Anybody have any ideas or things I could try? David

May 5th, 2006, 23:21	#6
dgbalfour VOC Member Last Online: Today 07:56 Join Date: Jan 2006 Location: Bedford	Metallic rattles Thanks for all your input, it's much appreciated. I would like to eliminate the alternator and water pump from the equation but I just don't dare run the engine without the belts for that long. Once you've shut it down for a couple of minutes to remove the belts it will need another couple of minutes running again to even consider rattling at you. It's very frustrating. However, the sound does appear to be close to the bulkhead from down low, around the bellhousing area. I will have another good look at the clamp that Peter mentioned and this insulation cover that I haven't found yet. There are no fault codes being recorded (yet). I'll be back with news when there is some... David

May 14th, 2006, 17:52	#10
charlotte001 Guest Location:	Or the air con It could be the air con pump too Charlotte

May 4th, 2006, 14:43	#2
Peter D Peter D Last Online: Mar 2nd, 2015 21:03 Join Date: Dec 2002 Location: Livingston	This could well be the cat itself and may not be doing it any good. Many cats are twin walled with a small gap to allow the inner to run at high temperature but I would have thought that running the engine whilst up on ramps allowing the Mech to listen would have identified this. Rest a screw driver on the cat casing and listen. The twin down pipe has a bracket welded to if which is attached to the gearbox, check this carefully as I have seen these corrode through and one of the pipe rattles in the bracket. You have checked the heat sheild I assume from both ends. I would also read your ECU Fuel and Ignition ( 2 and 6 ) for any fault codes just in case the knock sensor has died. Regards Peter

May 4th, 2006, 16:42	#3
Clifford Pope Not an expert but ... Last Online: Apr 26th, 2024 12:45 Join Date: Dec 2001 Location: Boncath	Have you eliminated the alternator and water pump from the possibilities? (Try removing the belts) Is it purely engine speed related, or does it depend on how hard it is pulling?

May 4th, 2006, 16:43	#4
ALLOA Master Member Last Online: Apr 25th, 2024 16:21 Join Date: Dec 2003 Location: ALLOA	David, I had a metallic rattle on the Torslanda that frustrated the hell out of me. Eventually I found it to be an insulation cover on the double pipe section of the exhaust prior to it running into the single length (between lamda probe and manifold). This appeared to have become brittle with heat and age and had separated from the spot welds. The cover was paper thin when I removed it. If this proves to be the problem with yours be careful ad there is a fine, flaky insulation material beneath. You probably don't want to breath any of it in!

May 6th, 2006, 07:38	#7
Clifford Pope Not an expert but ... Last Online: Apr 26th, 2024 12:45 Join Date: Dec 2001 Location: Boncath	Could it be the clutch release bearing or operating lever loose? You can access that by pulling back the rubber boot.

May 6th, 2006, 08:54	#8
Peter D Peter D Last Online: Mar 2nd, 2015 21:03 Join Date: Dec 2002 Location: Livingston	Good point Clifford but I would hope thathe has tried appying clutch pressure when he has the noise and the termal response time of the clutch assembly would be more then 2 mins but worth investigation. Regards Peter

May 13th, 2006, 21:38	#9
Les, slight limp Senior Member Last Online: Oct 21st, 2007 09:24 Join Date: Apr 2006 Location: walsall	I had a rattle that drove me mad, turns out a bolt had dropped onto the exhaust where the twin section is, used to rattle but only at a certain revs, have a quick look for a foreign object sitting on the exhaust below the geabox exhaust bracket, you never know.

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