Intermittent graunching noise
Discussion
I brought my sp6 Cerb into work this morning and not far from work I started getting a very distinct, intermittent graunching/hissing/grinding noise from the front/left/lower which is most audible through the gearstick surround. The closest I’ve known to it was once when I had a stick get caught in the wheel arch and rub on the wheel of my daily driver. Given the apparent location of the noise, I don’t *think* it’s auxiliary drive related.
However, this noise rises and falls with engine speed, comes and goes as if with the flick of a switch. It can last for a couple of seconds or up to a minute, and isn’t affected by shifting into neutral and coasting, foot off the clutch. It vanishes as suddenly as it appears and the car otherwise drives just fine, although I can feel a very slight hesitation when the noise starts – as if it’s adding a little load to the engine. For this reason I don’t think it’s the coolant bottle venting (temps are fine). I had been through some traffic but at the point when it started was cruising along at about 50.
I have a theory, but want to see if anyone has direct experience of the same thing?
However, this noise rises and falls with engine speed, comes and goes as if with the flick of a switch. It can last for a couple of seconds or up to a minute, and isn’t affected by shifting into neutral and coasting, foot off the clutch. It vanishes as suddenly as it appears and the car otherwise drives just fine, although I can feel a very slight hesitation when the noise starts – as if it’s adding a little load to the engine. For this reason I don’t think it’s the coolant bottle venting (temps are fine). I had been through some traffic but at the point when it started was cruising along at about 50.
I have a theory, but want to see if anyone has direct experience of the same thing?
A wheel bearing would make noise as a function of road speed, not engine revs, but thanks for the suggestion 
Pretty convinced it's something belt related given the way it comes and goes, but why it apparently comes from the left I can only imagine has something to do with the gear surround being the closest path for engine related noise?!
Pretty convinced it's something belt related given the way it comes and goes, but why it apparently comes from the left I can only imagine has something to do with the gear surround being the closest path for engine related noise?!
Silly question in this weather I know 'but' you didn't have your a/c running did you? This could give you your intermittent load on engine and if you have a gas leak on the high pressure side this would give you your intermittent hissing noise. Other than that perhaps a cooling fan failing or catching on something?
I had something similar, the noise became more frequent and eventually constant, so I took it to APM to investigate. The noise stopped a few miles before I got there. Andy pointed out that the alternator drive pulley had fallen off, if I remember the bearings had failed and the shaft snapped. It was an engine out job to fix. The car was ready for collection a few days later
Edited by FarmyardPants on Wednesday 7th January 22:32
Okay now I'm scared... is it an engine out to fix on the speed 6? There is a squeaking from the auxiliary drive but I haven't yet dug deeper to find out which bearing is doing it. Sounds more minor, eg the AC idler bearing.
Guessing the timing cover must come off, but if the operation is undertaken before the shaft snaps...?
Guessing the timing cover must come off, but if the operation is undertaken before the shaft snaps...?
If your unsure of the exact source of the noise tread carefully and avoid driving the car. Make 100% sure it's not the half time bearing producing the noise and the noise bouncing around the engine bay.
The auxiliary shaft sits on a plain bearing in the block, which the locates through a roller bearing in a bearing housing mounted to the side of the block that provides drive to the alternator and power steering.
The bearing housing can be incredibly hard to remove if its not been done recently. If the shouldered bolts holding it on are seized you'll want to sacrifice the housing and release the pressure round the bolts. If you snap the shouldered bolts off in the block, it'll likely be an engine out.
Edit:
Infact if you zoom in on some of the pictures in the thread on my profile you'll see the plain bearing.
The auxiliary shaft sits on a plain bearing in the block, which the locates through a roller bearing in a bearing housing mounted to the side of the block that provides drive to the alternator and power steering.
The bearing housing can be incredibly hard to remove if its not been done recently. If the shouldered bolts holding it on are seized you'll want to sacrifice the housing and release the pressure round the bolts. If you snap the shouldered bolts off in the block, it'll likely be an engine out.
Edit:
Infact if you zoom in on some of the pictures in the thread on my profile you'll see the plain bearing.
Edited by m4tti on Thursday 8th January 18:09
Stunned Monkey said:
Okay now I'm scared... is it an engine out to fix on the speed 6? There is a squeaking from the auxiliary drive but I haven't yet dug deeper to find out which bearing is doing it. Sounds more minor, eg the AC idler bearing.
Guessing the timing cover must come off, but if the operation is undertaken before the shaft snaps...?
You might be lucky if its the AC compressor or the steering servo pump, anything else is almost always an engine out job Guessing the timing cover must come off, but if the operation is undertaken before the shaft snaps...?
Remove the belt from the AC and you will see (hear)Peter
Hi guys, thanks for the replies. I'm happy to hear the internal bearing is plain and therefore unlikely to make this kind of noise, and hence if it is the support bearing, I should be able to swap it out in situe... Or an I being optimistic...? Thanks for the advice on the alternatives too, I will eliminate them first.
Just a couple of thoughts from me (S6 Cerb).
On an S6 Cerb the air con pulley sits just off the crankshaft balance(?) pulley at the front of the engine. A loose, corroded or dirty pulley could cause slight contact causing the issue?
I believe the cerb is fitted with a triple plate racing clutch. Has something come loose in the clutch, hence the noise in the g/box area and slight hesitation? Possibly some loose lining?
Possibly worth a post in the S6 section?
Hope this helps
On an S6 Cerb the air con pulley sits just off the crankshaft balance(?) pulley at the front of the engine. A loose, corroded or dirty pulley could cause slight contact causing the issue?
I believe the cerb is fitted with a triple plate racing clutch. Has something come loose in the clutch, hence the noise in the g/box area and slight hesitation? Possibly some loose lining?
Possibly worth a post in the S6 section?
Hope this helps
Hi Jules, thanks for the suggestions, I'll be sure to thoroughly investigate teh aux drive.
I don't think it's clutch related because the sound was not affected at all with the clutch in or out, pressure on the release bearong or completely off the pedal :/
I had thought about posting on the SP6 forum but the cerb forum is much more active. We seem to occupy a kind of no-mans-land with the Sp6 cerb! Nice to meet another owner
Martin
I don't think it's clutch related because the sound was not affected at all with the clutch in or out, pressure on the release bearong or completely off the pedal :/
I had thought about posting on the SP6 forum but the cerb forum is much more active. We seem to occupy a kind of no-mans-land with the Sp6 cerb! Nice to meet another owner
Martin
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