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ashman40
Samba Member
Joined: February 16, 2007
Posts: 15982
Location: North Florida, USA
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 Posted: Fri Jun 01, 2018 9:37 am Post subject: Re: Tensioning a new belt |
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| Spezialist wrote: |
| What’s the minimum number of shims between the pulley half’s, I forget? |
There is no minimum number of shims between the pulley halves. Well, I guess zero is the minimum as there would be no shims between the pulley halves and all the shims would be on the outside of the outer pulley. This would be a sign your fan belt is stretched and needs to be replaced.
You want as many shims as you can fit somewhere under the nut+cone washer, 10 normally but I'd go "no less than" 8 shims in total. Don't use more than 10 as you will start to reduce the number of threads the nut will be able to grab onto. As long as the end of the shaft is "flush with" or (slightly) extending thru the pulley nut once torqued down, you are good. If the end of the shaft is below the surface of the nut you should remove a few shims. Check this before you install the belt and you know you are setting the stack to the correct height.
This pic sort of illustrates the problem:
Imagine the shims + the pulley halves make up the area in blue. As you tighten the nut on the threads you compress the shims+pulley halves and form a solid stack BEFORE the nut runs out of thread.
If you leave out too many shims and tighten the nut you end up bottoming out on the bottom of the threads of the bolt (threads on the generator pulley shaft) and don't apply any compression to the shims+pulley halves. Even if the nut is torqued to spec you won't apply any pressure on the stack as the torque is being applied to the threads/bolt and not the stack.
This is why you use the max number of shims you can and move then from the inside of the pulleys to the outside so they remain under the nut and keep the nut from bottoming out.
In the above pic I would actually add a few more shims to move the nut further out on the threads to ensure I never bottom out on the bolt.
On my Beetle I could only fit 8 shims with the aftermarket nut+cone washer I was using. As long as you are certain that the nut is NOT bottomed out and has enough threads thru it to remain tight, you are good.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road  }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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Spezialist
Banned
Joined: July 01, 2005
Posts: 1941
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| Posted: Fri Jun 01, 2018 11:12 am Post subject: Re: Tensioning a new belt |
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| ashman40 wrote: |
| Spezialist wrote: |
| What’s the minimum number of shims between the pulley half’s, I forget? |
There is no minimum number of shims between the pulley halves. Well, I guess zero is the minimum as there would be no shims between the pulley halves and all the shims would be on the outside of the outer pulley. This would be a sign your fan belt is stretched and needs to be replaced.
You want as many shims as you can fit somewhere under the nut+cone washer, 10 normally but I'd go "no less than" 8 shims in total. Don't use more than 10 as you will start to reduce the number of threads the nut will be able to grab onto. As long as the end of the shaft is "flush with" or (slightly) extending thru the pulley nut once torqued down, you are good. If the end of the shaft is below the surface of the nut you should remove a few shims. Check this before you install the belt and you know you are setting the stack to the correct height.
This pic sort of illustrates the problem:
Imagine the shims + the pulley halves make up the area in blue. As you tighten the nut on the threads you compress the shims+pulley halves and form a solid stack BEFORE the nut runs out of thread.
If you leave out too many shims and tighten the nut you end up bottoming out on the bottom of the threads of the bolt (threads on the generator pulley shaft) and don't apply any compression to the shims+pulley halves. Even if the nut is torqued to spec you won't apply any pressure on the stack as the torque is being applied to the threads/bolt and not the stack.
This is why you use the max number of shims you can and move then from the inside of the pulleys to the outside so they remain under the nut and keep the nut from bottoming out.
In the above pic I would actually add a few more shims to move the nut further out on the threads to ensure I never bottom out on the bolt.
On my Beetle I could only fit 8 shims with the aftermarket nut+cone washer I was using. As long as you are certain that the nut is NOT bottomed out and has enough threads thru it to remain tight, you are good. |
Everett posted the picture to my question, 8 shims is the answer to the total number of shims required on a generator pulley assembly. Too few and not tight. Too many and not enough threads. It’s been so long I forget the right question. Thanks 
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Frodge
Samba Member
Joined: October 04, 2006
Posts: 1991
Location: Dump
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| Posted: Fri Jun 01, 2018 11:36 am Post subject: Re: Tensioning a new belt |
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| Is the generator nut 20 or 21mm? |
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