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A Puzzle for Friday, or a puzzle for life?

scam75

scam75

Active member
Hello all

So this grumbly noise issue I've had for years, simply refuses to go away. Quite often when the engine is cold, I'll get a bearing/grumble/scratchy/clicky noise from the alternator drive belt area. It goes away when the engine heats up. It also goes away instantly if I spray some silicone lubricant or the like on to the moving drive belt. So you would think the alternator or ac compressor bearing. Nope. Both changed at least twice and the noise persists. I've also changed the belt numerous times and also replaced the crank pulley, the old one was disintegrating. So every moving part in that drive belt set up has been replaced. The old crank pulley had started to strip and was depositing slithers of metal inside the belt grooves fyi. So what the fook is making this noise? Belts and rollers have also been changed and had no effect on this mystery happening. Could there be slithers of metal hiding somewhere? I genuinely don't think so. Why does the noise go away as soon as I spray lubricant in the drive belt area? I am totally perplexed. Fitted yet another re-con alternator the other day and there was no noise for a couple of days. Then it started back up again this morning. I am going demented, please someone come along with the solution!

Also posted this on TIPEC.

Cheers

Stuart
 
Are all pulleys in line?-Silicone spray solution albeit temporary would suggest alignment/belt tension problems to me.
 
Yeah was my next train of thought. I inspected the belt for side abrasions the other day and didn't see any. But it's the only thing that makes any sense. The belt seems to run true enough but maybe should examine closer. Strange thing is, when new alternator fitted on Wednesday, it ran perfect with no noise, had a right good look at it all moving whilst undertrays still off. So all back together and noise free for Wed evening and Thursday. Then Friday morning noise re-appears. The alternator spins true and can't really move due to how it is mounted. Same goes for the ac compressor, and I can't imagine how the crank pulley could get out of kilter. But then again...........

Thanks
 
It doesn't seem to be coming from there although could be wrong. It sounds very close to the alternator. Checked again and all seems to be in line and running true. Could it be the belt is too tight slightly, and loosens a fraction with heat? Out of curiosity I will loosen it a bit tomorrow. How much deflection should be on the belt at normal tension? Prob got half an inch at present in middle of belt. Anybody know how tight it should be and any methods for getting it spot on?
Cheers
Stuart
 
After I changed the cam/balancer belts I tightened the alternator belt to what I thought the tension should be. Turned out it needed to be tighter and made quite a racket....
 
Yeah this is doing my head in. I actually don't know how tight it should be. I've just been setting it to "seems fine". Need to know now to rule it out. Don't want noise and don't want slip and don't want to kill bearings either. Don't want much really!
 
When I started the engine after doing the belts and it was making that noise I thought sh*t. Traced it to the alternator belt and was very happy. I'd experiment with the belt tension and see if it helps. I'd also take the top timing belt cover off and have a listen in there, just to be safe...
 
Had a play tonight. Loosened belt a bit, noise worse. Tightened belt past last mark. Noise away. Seems loose belt to blame. How? Not got a clue. Undertrays back on, test drive. All good. Fingers crossed.

Stuart
 
I'll put one Mars Bar and a used first class stamp on the fact that Stuart's noise comes back within a week.

Anyone want to bet against me? I'll make that a King Size Mars Bar if it helps.

Anyone?


Oli.
 
zcacogp said:
I'll put one Mars Bar and a used first class stamp on the fact that Stuart's noise comes back within a week.

Anyone want to bet against me? I'll make that a King Size Mars Bar if it helps.

Anyone?


Oli.
Click to expand...


Make that Mick Jaggers Mars Bar....
 
If it comes back... Check the rear pivot bolt of the AC compressor. They have a nasty habit of shearing, as does the lug on the AC compressor. As for how tight... I think that on the Porsche tensioning tool it is "9" when the cam belt tension is "4.5", when it has AC fitted. I must admit I tension it until it stops squealing with everything turned on, and much less tension. The pivot bolts need to be slackened whilst tensioning it, otherwise if the pivot bolt doesn't shear, the AC compressor lug doesn't shear, then the adjuster probably will! I dare say you can guess how I know all of that!
 
Thanks for all your input chaps. Well Oli wins a Mars bar. The noise has returned but to a lesser degree and goes away very quickly after start up. Couple of minutes. I have checked the AC comp mounts and they are all good. Now clearly this noise lessens the tighter the belt is, but the belt is now quite tight, although no idea what "9" means, I can't help thinking going tighter is putting us into knackering alternator or AC comp bearings territory. Dilemma. Prob get half an inch deflection by hand on mid point between AC comp and crank pulley if anyone can decipher that vs "9" then well done! Also the noise is not belt squeal, its metallic, noisy bearing type noise. Still rescinds instantly with some silicone spray into belt area, which tells me it can't possibly be bearing noise, could it? Once again answers on a postcard to the great Scottish confectionary give away!

Stuart
 
Thanks Martin. Prob can go little tighter then. Will loosen a.c. comp and go again tomorrow.

Stuart
 
The alternator/compressor belt on these engines has to be much tighter than the usual 1/4 turn rule of thumb.
10mm of deflection on the longest stretch also sounds good to me.
 
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