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Discussion Starter · #1 ·
Changed the belt last winter, as I thought it was due on time. No issues for 10k+++miles before new belt.

200miles with the new belt, and battery light came on, belt gone. Went back and found it. Shredded.

Inspected all 3 pulleys, and noting to see.
Installed a new belt, 60miles, shredded again. failure looks identical.

Both times the fail occured right after a hard acceleration.

I tension belt to spec. 140hz. Did sanity check with the old fashion 90 degree twist test. Seem all good.
First belt Dayco 5PK946 from eurospares
Second 5PK950 local sourced, german made.

ANY ideas?!🤷‍♂️🤷‍♂️🤷‍♂️
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Yes, verify pulley alignment first. If one is off, likely bearing or component is failing. If they are all in alignment, check pulley surfaces for irregularities. I had similar issue in another car that turned out one of the smooth idler pulley's wasn't so smooth anymore at one end and was turning belts into black spaghetti
 

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Discussion Starter · #5 · (Edited)
Did some more checking.

It is a simple system; crank pully, alternator pully + a manual tensioner.

Both bearings are fine, no noise, no play.
Both pullys show no damage.
Tensioner still tight.
Checked pully alignemt with straight edge, looks good.
I see nothing that can come in contact with the belt.

Looking at the wear marks on the tensioner pully, it looks to have run offset from center of belt.
Matching it to the original belt it might even run over the edge. Looks like this has been the situation from day 1 though…




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That could be it, belt riding on the edge of a pulley will eventually fail starting from the edge. May seem fine at idle, revs. but varying loads while accelerating and downshifting belts do move around slightly. For lack of anything else obvious I'd look into replacing the tensioner, especially if you notice any front to back (end play) in it............
 

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Here's a pic I found of a used tensioner, looks like the belt was more centered on this one. So either somebody forgot to put a washer back somewhere along the way causing misalignment or something's off with that tensioner
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Discussion Starter · #8 ·
I agree, and already ordered a new OE tensioner.
I also studied some used parts, and found the same, the belt should be on the center of the tensioner pully.
There is no play in the current tensioner, and it is not bend, as far as I see and measure.
 
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