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Overtorqued
Bad bolt (casting flaw in the steel)
Bad thread in the crank
Magic
Bad luck
Gremlins

In that order
 

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Discussion Starter #4
really, i would have put gremlins first?


what did you toghten it to?
I didn't tighten it. It was done in a garage about three weeks ago !! Rebuilt with a BRAND new crank and a new stretch bolt. I was travelling along a motorway this morning at about 60 mph when I heard something hit the bottom of my van , I thought I had run over something, I looked in the mirror and saw the bottom pulley careering up the banking !! By this time the engine had obviously stopped, when I pulled up I checked and every belt had disappeared .

At the end of the crank, where the stretch bolt fits, I can still feel the remains of the bolt!! So as you can imagine I want to get my ideas on why it went wrong before I go and see this mechanic in the morning !!

If anybody has any thoughts ? They will be gladly welcome.

Phil T:
 

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Would be good to look for the bits and try and recover the other part of the bolt. the shape of the break could give an indicationa and also you should be able to see what grade it was by the marking son the head. It's possible that the wrong garde bolt was used.
 

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Discussion Starter #6
Would be good to look for the bits and try and recover the other part of the bolt. the shape of the break could give an indicationa and also you should be able to see what grade it was by the marking son the head. It's possible that the wrong garde bolt was used.
I've not got much chance of that. It would be like searching for a needle in a haystack !!


Phil
 

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If this happened while the van was running, it is possible that the bolt unloosened itself enough caused the vibration pulley to wobble around so much that it caused the bolt to snap and took out all of the belts at the same time. The vibration pulley is a substantial mass and could easily cause a bolt to snap if it was rattling around freely on the end of a loose bolt.

I said earlier "overtorqued", after your description i think it has been undertorqued and or the diamond washer has been left off. Not sure how to go about proving this though. The fact that you had the work done at a garage so recently leaves them with no comeback though. Even if it is just a fault with the new parts, they would be obliged to repair the damage and they will have insurance to cover these problems and they should be able to get something back from their parts supplier.

Pain in the rear....yes, but you should be able to get it fixed at their expense, keep us updated.
 

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If this happened while the van was running, it is possible that the bolt unloosened itself enough caused the vibration pulley to wobble around so much that it caused the bolt to snap and took out all of the belts at the same time. The vibration pulley is a substantial mass and could easily cause a bolt to snap if it was rattling around freely on the end of a loose bolt.
I would agree with this. I have changed belts on my T4 & wifes Polo[previously changed by VW] & both weren't tight enough when I undid them. The torque on the T4 is so it's hard to achieve using proper tooling it's unlikely to be overtightened.
It's also possible that a genuine VW stretch bolt wasn't used but something with a lower grade as has been suggested.
 
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