C5 X7 HDi V6 aux belt vibration - Alternator Change

[wurlycorner]

Another query on this infernal thing…
Since I bought it, I’d been hearing a vibration from the engine bay at idle, which is basically there throughout, but comes and goes in intensity. Disappears when revs increased.

While under the car with undertray off, engine running, attempting to diagnose the engine mount issue, I spotted the cause - the aux belt is vibrating badly on the bottom run between the a/c and crank pulley and this is the cause of the noise - see video below.
It doesn’t take much to stop it (you’ll see me lightly run the work light against it and instantly stops).

Is this normal on an HDi V6? I feel surely not.



I replaced the idler pulley recently because the bearing was knackered. OEM part and while the belt was off I checked all others and condition of the belt - no issues anywhere, belt appeared to be not that old and was a good brand. Tensioner seems fine, no excessive slack anywhere.

I’m not sure if the crank pulley is running true - are they known for causing issues? I note it is a harmonic damped pulley but looks ok to inspection? I spanner checked the main crank bolt and the smaller bolts that bolt the outer part of the pulley to the inner and all seemed tight.

[PaulC5]

You cold put a white line across the pulley and see if it stays lined up as the engine runs.

[the-termin8r]

I haven't noticed such a noise on mine. How noticeable is it from inside? Would I have to specifically be listening for it or would it just sound like it doesn't belong immediately?

Based on the video, it looks like the "left" pulley is forcing a vibration / oscillation of the "bottom" half of the belt. Could the pulley be slightly misshapen and closer to being elliptical than circular in the section? When you inspected the belt, I assume you checked both sides, but it could be an imperfection or manufacturing defect in the belt. Or maybe some debris could have somehow gotten embedded in the belt. I'm just guessing here, but probably best not to rule out the weird or unlikely yet.

[wurlycorner]

Hi Rob
It's not very noticeable inside the car at all, but it is noticeable from outside near the engine bay - especially with the bonnet up.
I'm sure you would notice it, if it's there on yours.

I checked both sides of the belt, yes. I didn't fully remove it out of the car though, only inspected it while it was still hanging beside the engine so there are sections of it I didn't see - it is CRAMPED to work on in there and it was late in the day so I didn't fancy pulling it all the way out and regretting it due to being unable to refit (it would be slightly easier now, with the undertray off). It would have to be very localised damage to the belt, because the rest of it is just perfect - though that is possible, as you say.

I guess my next port of call is unfortunately to pull the belt all the way off (sigh) and then also do a better inspection on the harmonic balancer with a scope camera.

[the-termin8r]

Yeah, the space constraints are crazy, I thought my 2L was tight, but looking at it now, it has a couple of chasms you could hide entire civilisations in in comparison. I'll go out to mine later today and have a listen, I can't get under it though as I don't have a proper jack or stands.

[wurlycorner]

I'm hoping for your sake you don't have the same issue.

We should probably meet up and compare notes on the two basket cases we bought

[the-termin8r]

I'd be up for it LOL. I've booked mine in for yet another appointment on 2/6/25, this time to get bigger stuff done. Major service, brake and transmission fluid, belts and a couple of other bits I forget off the top of my head.

[MattBLancs]

I believe a seized alternator "clutch pulley" can lead to such belt flutter. It might be worth whipping the auxiliary belt off and confirming the alternator pulley does do the (slip one direction, no slip the other) sprag clutch action it is supposed to do.

Chalk/paint line across the crankshaft pulley as suggested is also a good test

[MattBLancs]

Not watched this all through, but shows what I describe I think:

[wurlycorner]

Really great info and suggestion there Matt, thanks.

Just been out and checked and the tensioner is vibrating slightly, but nothing like in that video. That may well be because of where in the run the tensioner is located in comparison to the alternator though (sketch I used on the forum previously). I guess it would quite reasonably show up more on the bottom run after the A/C.

If it is that... Argh, where to go for a replacement.
On a quick check: not listed in gsf; eurocarparts; eurocarcare; free wheel clutch is NFP at AutoDoc, so onto a new Alternator from them which is £381 for a brand I trust...
The money pit continues!

[the-termin8r]

Iain, I just had a look at mine. Didn't hear anything out of the ordinary, but I did notice that the idle revs seem to almost "breathe." It sound like they go up and down ever so slightly, so I wouldn't call it hunting, tacho doesn't even pick it up, and the frequency and "amplitude" stay constant, so I'm assuming it's normal. That and what sounds like a faint high pitched whine, like the screen wash pump almost. However, I've heard that sound on videos of other cars with this engine (such as here), so I'm assuming that's normal too. I'm still getting used to this engine's noises.

[wurlycorner]

Thanks Rob.
I can't say I've noticed that - though the current vibration noise might well be masking it
Will update once I've been able to get the belt off/inspect and to check the alternator free-wheel clutch pulley.

[wurlycorner]

And the alternator clutch pulley is indeed the culprit.
Thanks very much for the heads up there, Matt.

But FML this thing is beyond taking the mick (see other post updated today...)

Does anyone have the alternator change procedure for a 3.0 HDi please???
(I have horrific visions of needing to take the front of the car off in order to get to it, but would at least like to know the relevant torque settings as well please).

[MattBLancs]

And the alternator clutch pulley is indeed the culprit.
Thanks very much for the heads up there, Matt.

Ah, that's great - I'm really happy to have saved you from changing say tensioner and/or harmonic dampener pulley etc to no avail!

I've swapped alternator on my 2.2 HDi, but suspect that different enough to your V6 as to offer not much help or tips.

I suspect it's awkward enough to make having a new complete alternator is the sensible way forward, pulleys are available separately otherwise

[wurlycorner]

I did look for new pulleys but couldn’t find one (still available - found old listings) for the alternator on this engine.