Noisy aux belt tensioner c5x7

[aerodynamica]

Hi all, C5 2.0 Hdi auto. I've noticed a lot of noise from the alternator area upon start up - at its worst when fans, lights etc are on.

Aux belt new only few months ago and I thought the alternator was failing but now I'm sure the noise is actually the belt tensioner below the alternator. Can see it shaking slightly with the noise.

I recall it has a stiff spring to push the tension but can't recall if it was locked after tensioning like on cambelt. Anyone know if the tensioner is meant to shake like this? Is it one of the 'floating ' type?

I really should recall from changing the belt but I've forgotten.

[GiveMeABreak]

Yes, the alternator has a dynamic tensioner and must be locked with a pin prior to changing the belt.

Tensioner at (6)

[aerodynamica]

Hi Marc, thanks for this. I recall the locking of the tensioner to remove the belt ( made a special tool for this) but is there any information on the tensioner itself such as can the spring be adjusted an any way? I realise it's meant to move but the sound it is making sounds a bit wrong. Might need a spray of WD down where the tensioner mount meets the engine block.

[Lenny]

Check the pulley on the alternator.
They're supposed to have like a freewheeling clutch mechanism in them but eventually it fails and makes the belt judder.
Not a bad thing to change (with the right tool).

[aerodynamica]

Oh there's a thought Lenny.

[GiveMeABreak]

No manual adjustment on the dynamic tensioner - as it's supposed to be 'dynamic'. It's compressed first, then pegged as you know, then belt replaced, locking tool removed, then the tensioner slowly decompressed using the tool.

If it's nothing else like the alternator pulley, then I suspect the dynamic tensioner may need replacing.

In anticipation of replacement, the part was superseded, so may be a reason.... anyway the new part number ((6) on the diagram), is 1611424380, £152.88!!

[dulenator]

I had a bad alternator pulley, and the tensioner was jumping like crazy, matching the clicking sound. It looked like the tensioner was going bad, so I changed it, and the new one was doing the same. The alternator pulley fixed the issue.

[aerodynamica]

I had a bad alternator pulley, and the tensioner was jumping like crazy, matching the clicking sound. It looked like the tensioner was going bad, so I changed it, and the new one was doing the same. The alternator pulley fixed the issue.

Thanks, it certainly is the most cost effective solution. I think I will order the pulley clutch to replace and see how that turns out. Alternator output is fine so I suppose the Alternator itself is ok. Thanks again

[nimi62]

Hi

Also had same problem with Jumpy II and tensioner replacement didn't fix the issue.
Car has driven over 300tkm, so seen that alternator replacement as DIY was cost effective solution as new (refurbished VALEO) from Autodoc paid only around 200€.
Alternator had still need to be removed as the belt-clutch was that near the car body that replacement there wasn't possible.

So replaced whole alternator, which fixed also tensioner issue.

[Ttron]

I was going to start a new topic but my issue appears to have been covered here.
My 2016 C4 HDi (which I have had for less than a year - it's done just over 50,000 miles) has this issue of the 'chattering' aux belt tensioner. I am guessing it had been doing this for some time before I got it as the top tensioner (mine has two!) was lying at a bit of an angle suggesting the swing bearing had had enough.
I fitted a new belt & tensioner kit (Gates) a few months ago but sadly this didn't cure the chattering problem. Loading it up (A/C, lights, blower fan, PAS etc.) didn't seem to affect it. What DID stop it was some WD40 on the vee side of the belt - but only for 30 seconds or so then back it came. It's worst at idle speed.
I've had the new belt off, thoroughly cleaned it and all the pulleys and it's still the same. I even tried the old belt back on in desperation!
What I have also noticed is the stop/start seldom activates now, I don't know if it's connected but I'm not that bothered about that.
Having looked at @GiveMeABreak 's diagram above I just had a quick look at my setup to see if it's the same - which it's not! Mine has two sprung tensioners, one either side of the alternator pulley. BUT what I have now found is where there should be a bolt securing the alternator pulley, there is a welded 'blob'! Grrr. (I already had reservations about the previous owner's choice of garage....)
So may we be looking at replacing the whole alternator?
I will attach a pic, apologies for the poor quality, it's kinda hard to get a decent photo due to the pesky chassis leg in the way!

[aerodynamica]

Hi Ttron, I'm not sure what might be causing yours - I replaced the pulley on the alternator itself and it has cured the noise. The old pulley was very badly seized when I tried to move the freewheel of the pulley. I'm looking at your photo and the visible pulley appears to be a different type - not like a 'clutch/ freewheel' type.

[Ttron]

Hi Ttron, I'm not sure what might be causing yours - I replaced the pulley on the alternator itself and it has cured the noise. The old pulley was very badly seized when I tried to move the freewheel of the pulley. I'm looking at your photo and the visible pulley appears to be a different type - not like a 'clutch/ freewheel' type.

Thank you for your input @aerodynamica . I have no way of knowing if this is the original pulley, and even if it is, what's been done with it in the past. I've already had reason to question the previous owner's 'trusted' garage's methods. (I.e might it have been a clutch/freewheel type before being butchered?). To be fair though the alternator did spin very freely when I had the belt off - and probably in both directions as I cleaned it very thoroughly (though I wasn't consciously checking for that).
When you say "freewheel" should it be like a bicycle freewheel such that turning the pulley backwards would not turn the alternator shaft?

[myglaren]

My C5 had a persistent belt squeal that turned out to be the alternator clutch/freewheel pulley. A cheap fix at £30.
But it also needed a new belt and crankshaft pulley, ruined as it had gone on so long.
£160 all told.

[aerodynamica]

Hi, yes it's much like a bicycle freewheel. My old one was virtually seized although it was only once it was off that you could actually tell. I'll be honest, I'm not 100% sure what the freewheel system does - possibly purely a smoothness refinement. Although I considered it was an attempt to allow the alternator to spin faster than its drive belt at times when the engine slows e.g with engine braking. I'd have thought that was less likely since the alternator is almost always under load. Would be interested to know if anyone knows for sure.
I'm not sure the garage would have swapped the pulley with the wrong type because the freewheel variety have quite a specific fitting. Although it's not impossible.

Perhaps if you search the exact part number you might get an image of the correct item to compare to the one on your car.

[Ttron]

.................
Perhaps if you search the exact part number you might get an image of the correct item to compare to the one on your car.

Thanks again aerodynamica. Yes, part numbers are wonderful things - except the sticker (if it's still there!) is in the most awkward, inaccessible place. Something the seem to excel at!! I might dig out an old Android endoscope, see if that can see it.
I wonder if the freewheel/clutch mechanism could have something to do with the stop/start. I read on the C4 forum that some systems use the alternator for 'warm starting' and I wouldn't be surprised if this was the case here, as on the odd occasion the S/S did work, it didn't sound like the normal starter was engaging.