Snapping belts and busting pulleys

[Steve68type3]

I’m having problems with my Squareback, it keeps snapping belts and busting pulleys constantly, I recently replaced the generator and redid all the hardware on the fan and case because it kelps snapping belts when I go over 55 mph anyone know why? Also keeps busting my pulleys… I’ve adjusted the generator and still keeps busting belts and pulleys… wonder if anyone has had this problem or has the same issue… thanks

[nogoodwithusernames]

First thing that it sounds like is misalignment, can you put a straightedge along the belt and both pulleys are nice and square with each other? Possibly too much tension on the belt?
_________________
71 Squareback, 1.7l T4 w/ crank trigger fuel and spark
(Conversion thread https://www.thesamba.com/vw/forum/viewtopic.php?t=732508&highlight= or https://shoptalkforums.com/viewtopic.php?f=1&t=151375&sid=f0542d44a322d290c29d6609fac7f215 )
74 914, 2.0L w/ D-Jet

-Derek

[blues90]

That looks like the out side gen pulley has the shaft opening beaten out of shape. I've never had this happen. The only way I can see it is if the gen bolt was not tightened up well. If you did the other hardware I would think you know how to fit that pulley and shims. All I find when changing of adjusting the belt is in order to get outer pulley against the belt proper and fully tighten the nut i need to rotate the nut as I turn the pulley so the belt is home.

[Steve68type3]

So far I’ve done the alignment on the pulley and fan where the belt goes, the parts I’ve replaced are the internal fan, generator, generator pulley, I was told maybe the fan where the belt goes on my be bent?

[hazetguy]

that pulley is garbage and should not be used any further. while the outside lip is pretty beat up, the more important thing is that the center opening is completely damaged. this wear is caused by the pulley not being tightened properly and the two halves of the pulley rubbing back and forth / flopping against each other over time. i'd also bet that there is a significant groove on the male hub section on the other half of the pulley. there is also fretting / friction wear where the special cap seats, and that's another thing that tells me that the pulley hasn't been tightened properly.
it is crucial to have the proper amount of shims on the pulley. if you don't have enough, this can cause the damage you have, because while you think you are tightening the pulley nut all the way, there will not be enough pressure holding the two halves together (again, causing the damage you have).
another thing to check is the special cap that the pulley nut tightens against. sometimes those will hit the generator shaft and you will get a 'false' sense that the pulley nut is tight when it isn't. again, this can be eliminated by having the correct number of pulley shims, and shims in good condition.
other things to check are the condition of the keyway slot in the generator shaft (key whould be a tight fit in it, no wiggle), the keyway slot in the male part of the pulley hub (no rocking of the pulley when installed on the key / shaft) , and the condition of the half-moon key itself (they can get worn if there is excessive pulley movement).
post some pics of the other part of the pulley and the special cap.

here are some pics of how the center part of the pulley and hub should look. notice the crisp lines, and the lack of marks on the male part of the inner pulley half hub section.

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[Bobnotch]

Yup there should be 7 shims to set belt tightness of gen pulley. Not all are used between them, and those not being used get "stored" under the stepped washer under the pulley nut. You might not have enough shims between the 2 parts of the pulley causing it to "grab" the belt causing the problem.
I hope this helps.
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71 Notch ...aka Krunchy; build pics here;
http://www.thesamba.com/vw/forum/viewtopic.php?t=249390 -been busy working
64 T-34 Ghia...aka Wolfie, under construction... http://www.thesamba.com/vw/forum/viewtopic.php?t=412120

[KTPhil]

As posted, it is easy to THINK you tightened it, but it is cocked a bit and will loosen, leading the belt failure and pully damage. With it all under the cover you don't notice as easily as with a Bug. They also wear out! The one shown has significant wear at the point the belt rides, as did mine.

I leave my T3 belt on the loose side. It is just running the gen load , not the fan, so it doesn't need a death grip. But the pulley halves must be absolutely tight, however.

[Steve68type3]

Thanks for the help, just placed an order for a new pulley, is there a way the shims go? I had 3 on two on the inside and one on the outside… maybe it’s been wrong the whole time

[mdege]

You have to have a total of 7 shims. The shims are use to set the belt tension.

If you need more tension you take out a shim from in between and store it on the outside and vice versa if you need less belt tension.

But remember you always have to have a total of 7 shims in the stack.
_________________
- Michael

1965 21F: Restoration of a former '65 firetruck
1963 Typ3 Notchback project
1988 Multivan Magnum 112i
1984 Standard: My son wanted a bug for his first car

[blues90]

If you only had 4 shims as the others have said you need 7. You can get shims. I also leave some slack in the belt so it slips if you try to turn over the engine using the gen nut. Or once the belt is installed there should be slack in the belt between the gen and engine pulley. You do need 7 shims , if not you can never tighten the gen pulley enough.

I should have been more clear before.

At least now once you have the new pulley and 7 shims this issue will be over.

It does require you to fiddle to find the proper amount of washers to get the proper belt tension when you start from scratch. And as said here that cap that the gen nut fits against has to be on the gen shaft flats . I would check to make certain it did not get damaged along with the pulley. If you don't it will present a problem.

[74 Thing]

Shims come in different thicknesses so to say you need x number of shims is incorrect.

What you need to to is start with enough shims in between the pulley halves and when you tighten the nut all the way the belt is still loose.

The correct procedure it to take out 1 shim at a time and place it on the outside of the outer pulley and tighten until you reach the right deflection. If you do not do it this way there is a chance the pulley halves will not be tightened correctly and instead you are tightening the pulley halves against the belt which will cause them to loosen up when driving and oval out the pulley hole.

[blues90]

The stock shims are .5 mm thick. If you get the 10 shims in a pack they don't state the thickness all it says is use all 10. I'm sure you can use more between the nut and cap as long as the nut has enough threads so the shaft is past the nut and not level with it.

The main thing is to get the right amount of shims between the pulleys so the belt has some slack then see how many it takes to stack between the nut and cap and still have at least over 1/8" of gen shaft threads showing.

The Bentley states 7 shims as long as they are the stock thickness.

[KTPhil]

[blues90]

[74 Thing]

https://www.thesamba.com/vw/forum/viewtopic.php?t=767536&highlight=pulley+shim+thickness

There is plenty of posts about it, but just put a mic on yours. Some of the crap aftermarket ones are all over the place on thickness.

Regardless, use as many as you need so that when tightened down the pulley halves and the shims are the parts that are compressed and not the belt. As I stated about, the right way is to put to many shims in between the halves when tightened down and then remove one at a time until you get the right deflection. By doing it this way you are assured to not make the mistake of tightening against the belt.

[Bobnotch]

[Steve68type3]

I installed a new original pulley with a German belt I got from isp, I also forgot to mention the car only snaps the belts if I go on the freeway and do 60+, I recently retapped the housing in what the internal fan goes into because it was causing it to rattle, but so far so good seems to be ok I did add all the shims