C5 X7 Alternator Question

[admiral51]

Hi All.
Just a little history to explain the question.
The Aux Belt tensioner has become very noisy and acting like a pogo stick so needed to get that replaced along with the Aux Belt.

However the diagnosis is that the Alternator Pulley is at fault but not the main Pulley but a free wheeling pulley that has siezed and putting extra strain on the Tensioner.

So can someone explain to me what this actually is and how it works as in the attempts to remove this pulley bolts have been sheared and now looking at a new Alternator at a cost of £300 + Vat just for the Alternator

Is it possible to run the Alternator without this Free Wheeling Pulley, will it affect the charging and or damage the belt ?

And no it was not at my trusted garage they were too busy

It is for the C5 in my signature so if anyone can post part numbers and diagrams i would be very much grateful

Colin

[admiral51]

Just a very quick update on my original post

I have done a little bit of digging and the pulley is siezed in situ so in effect the alternator is going to be needed to be changed as from what i understand the free wheeling pulley is there for damping reasons and nothing to do with charging but would still like some of you experts to confirm deny

Colin

[Lenny]

Hi,
I've had the same problem but in all honesty the fix was quite easy and cheap.
You'll never do the job without the correct tool though unfortunately...

https://www.ebay.co.uk/itm/351749023192

...I'd imagine trying to get the pulley off with anything else would be more than a bit challenging. It's stupidly tight.

[Lenny]

I read somewhere that this freewheeling pulley should almost be classed as a service item.
Gates (the belt manufacturer) state that the pulley has the same life expectancy as the belt so they should be replaced together but that rarely happens.

[xantia_v6]

When the battery is fully charged, the alternator is not taking any energy from the belt, with a fixed Pully the alternator rotor is just acting as a flywheel connected to the crankshaft by a rubber band, causing resonance in the belt and tensioner.

For 100 years this was not a problem, but now it is.

[MattBLancs]

Yes they can seize and in effect become a solid pulley.

Yes also quite correct they are dampening load on the belt.

Short version: a running engine isn't ever actually maintaining a fixed speed. Instead it alternates between acceleration (when one piston is on the power stroke) and deceleration. If consider a single cylinder engine, the other three strokes are slowing the rotating components down:
intake, dragging the piston down, pulling air in through the open intake valve,
Compression: squashing the air mixture,
(Power stroke speeds it all up again)
Then exhaust, pushing the exhaust fumes out into the exhaust system.

Obviously a 4 cylinders has each piston firing at a different time and this shortens time between acceleration and deceleration. Nevertheless, engine IS accelerating and decelerating continuously.

Now imagine the auxiliary belt, driving the alternator (and other stuff, but ignore that for the moment)

Alternator needs to spin fast, so is often smaller pulley around half the diameter of the crank pulley.

So the acceleration and deceleration effect is doubled and the alternator is being asked to speed up and slow down quite severely.

This is hard work for the belt which drags the alternator up to the higher speed (high belt tension between crank and alternator) the suddenly, engine is slowing down and the fast alternator is now wanting to continue at its high speed. So belt tension between crank and alternator drops right off. In effect belt goes tight - slack - tight - slack endlessly.

Then the cycle repeats again and again.

So, the alternator clutch pulley allows the alternator to freewheel - just like a bicycle freewheel hub - and so it go faster when pulled along then freewheeling at higher speed (obviously it does slow somewhat as the alternator is turning rotation into electricity) but it decouples from the engine speed until it's slowed and the crank speeds up (and belt with it) to then "kick it along" again at high speed.

This obviously removes the tight - slack belt fluctuations.



So. Knackered pulley, locked solid, no longer does this job. Belt now again in the tight - slack - tight scenario again.

Net results:
Tensioner has a hard time and can often be seen dancing about.
Belt has a hard time and so more likely to snap long before it's expected life.


Seems a simple and almost unnecessary item, but clutch pulley has an important job to do.

Ok, will stop waffling, let me know if does not make sense and I'll make various excuses about autocorrect on the phone garbling my words for me!

Matt.

[Lenny]

Cheaper tool here:

https://www.ebay.co.uk/itm/125432049344 ... R6TH057TYQ

[admiral51]

I knew you lot would give me the low down from your expertise and i thankyou all.
Unfortunately the car is at the garage so i really appreciate the pointers Lenny but was a needs must and now i have to pay the piper
Yes everything makes sense all i need now is a kind person to post the part number for the alternator and pulley ( Guess they will be seperate ) so i can find a way to keep the costs down a little bit.

Colin

[xantia_v6]

I suppose you did ask your garage if they have the pulley removal tool set? If not, it may be cheaper to buy them the tool than a new alternator.

[admiral51]

I suppose you did ask your garage if they have the pulley removal tool set? If not, it may be cheaper to buy them the tool than a new alternator.

No was a needs must as my trusted garage were busy and these are just across the road, kind of needs must but going to be some interesting phone calls tomorrow

Colin

[myglaren]

I had a similar problem with one of my C5s, a constant squeal. The people who were supposed to be doing the servicing and repairs could never fix it other than spraying belt wax on the belt, that worked for an hour.
Took it to a recently opened garage run by the Polish friend of some of my workmates.
He knew what it was as I drove in. Fixed the next day but did cost rather more than he had estimated as it had gone on so long it had ruined the crankshaft pulley (dual-mass). The new clutch was about £30 and £160 all in.

[MattBLancs]

. Fixed the next day but did cost rather more than he had estimated as it had gone on so long it had ruined the crankshaft pulley (dual-mass). The new clutch was about £30 and £160 all in.

Interesting!

I thought the alternator clutch pulley did away with the need for a dual mass crankshaft pulley and it would just have a solid conventional pulley instead, but you'd both!

Two independent sources of potential failure in one belt system! (or in your case not independent as one had knackered the other!) Oh well, glad was fixed properly rather than keep treating the symptom instead