The top pulley on my alternator decided to unthread itself on the way home from Telford today. Thankfully the pulley was sat in the chassis rail still and the belt is still there too.

Question is, can it just be bolted back on? Heard something about a sezied over-runner, and wondering if that means replacement alternator? I have one from a PD130 Ibiza as it happens.

The alternator pulley has a one way clutch (sprague) in it, which allows it to freewheel in one direction. When they seize up I've seen snapped auxiliary belt tensioner arms as the symptom. Alternator pulleys are replaceable on their own.

i thought the over runner was so your alternator wound its self down when you stop the engine and doesnt just stop dead ....

I might just fit my replacement one I have, I know its lower miles than the one bolted on now. Will have a better look another time.

Did it come off completely or is the middle bit still attached to the alternator?

Here's a photo I just took. Thread in foreground, pulley down in chassis rail. I was lucky not to lose it.

Lucky that. It would appear that the whole pulley has just unwound off the alternator. Could it be that it wasn't attached properly.

Last one I took off involved strapping the alternator to the bench have one spanner braced against the bench and then using a scaffold pole over the end of a breaker bar to get the bloody thing off. And that was after an evening soaking in penetrating fluid.

You need the proper tool to put the pulley on and if you have a spare alternator it may be quicker just to fit that.

If you retrieve the pulley and take off the plastic cap there is a part number (not a Skoda part number) stamped on the end and ECP/GSF will be able to supply you with a new pulley based on that.

The alternator pulley has never been off the car/alternator before, so something has caused this - the above mentioned item being seized is a ilkely candidate.

Having just seen the photos on Brimma's thread it could have been the same forces that did for your tyres.

If it has seized then it was lucky it didn't shear in two as they seem to have a habit of doing. I would look to change the belt and tensioner whilst you are sorting this. IIRC the tensioner is less than £30. Also it is dead quick to swap.

i told you not to go so fast in reverse :p

I never would have thought cornering would cause this, but I was cornering as quickly on Saturday as I have ever done before thanks to the phenominal grip from the tyres.

As I mentioned before, in order to loosen the pulley on my old car I was bouncing up and down on the end of a 6ft scaffold pole with the alternator strapped to a bench, and I'm not little, so to see it unscrew itself is a surprise.

I never would have thought cornering would cause this, but I was cornering as quickly on Saturday as I have ever done before thanks to the phenominal grip from the tyres.

What tyres?!