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radbug69
Samba Member
Joined: June 11, 2020
Posts: 199
Location: Maine, North East USA...
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 Posted: Wed Aug 13, 2025 5:10 pm Post subject: Generator belt adjustment shims, starting point...? |
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'69 Beetle...
While waiting for a new, replacement Voltage Regulator, belt and shims, (thanks for you folks input diagnosing that) I removed the old one and made a note of the number of shims, five behind the outer pulley half...
Is there a rule of thumb for quantity to start with to adjust the fan belt correctly...?
Thanks much,
Rob |
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bsairhead
Samba Member
Joined: October 08, 2008
Posts: 4556
Location: viroqua wi.
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| Posted: Wed Aug 13, 2025 5:48 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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| I do 6-2. If it needs more than 8 between the halves I find a different belt. |
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Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 80418
Location: Sneaking up behind you
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| Posted: Wed Aug 13, 2025 5:52 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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I like to run a slightly shorter belt, that way the belt sits lower in the pulley and the fan spins a bit faster.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare
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Cusser
Samba Member
Joined: October 02, 2006
Posts: 33457
Location: Hot Arizona
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| Posted: Wed Aug 13, 2025 6:35 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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I'd start with 5 shims, and go from there. I'm an outlier on this subject as I have intentionally run my generator belts a little looser than specifications on both my 1970 and my 1971, to save wear and tear on generator bearings.
I'm in Arizona, and have not had either charging issues or overheating issues either. When I need to check/adjust valves, I simply push in on the belt a little as I turn the generator pulley with a wrench.
1970 1600cc DP
1971 1835cc DP
_________________
1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297
Last edited by Cusser on Wed Aug 13, 2025 6:38 pm; edited 1 time in total |
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bsairhead
Samba Member
Joined: October 08, 2008
Posts: 4556
Location: viroqua wi.
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| Posted: Wed Aug 13, 2025 6:36 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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| Glenn wrote: |
| I like to run a slightly shorter belt, that way the belt sits lower in the pulley and the fan spins a bit faster. |
I run the recommended size and drive appropriately. |
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Glenn
Mr. 010
Joined: December 25, 2001
Posts: 80418
Location: Sneaking up behind you
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| Posted: Wed Aug 13, 2025 6:38 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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| bsairhead wrote: |
| Glenn wrote: |
| I like to run a slightly shorter belt, that way the belt sits lower in the pulley and the fan spins a bit faster. |
I run the recommended size and drive appropriately. |
Sorry, I have a 5 speed so doing only 60mph in 5th has the RPMs a bit low.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare
עַם יִשְׂרָאֵל חַי |
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bsairhead
Samba Member
Joined: October 08, 2008
Posts: 4556
Location: viroqua wi.
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| Posted: Wed Aug 13, 2025 6:55 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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| Glenn wrote: |
| bsairhead wrote: |
| Glenn wrote: |
| I like to run a slightly shorter belt, that way the belt sits lower in the pulley and the fan spins a bit faster. |
I run the recommended size and drive appropriately. |
Sorry, I have a 5 speed so doing only 60mph in 5th has the RPMs a bit low. |
"Sorry, i have a 5 speed" well ta-ti-da to you. |
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Glenn
Mr. 010
Joined: December 25, 2001
Posts: 80418
Location: Sneaking up behind you
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| Posted: Wed Aug 13, 2025 7:17 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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| bsairhead wrote: |
| Glenn wrote: |
| bsairhead wrote: |
| Glenn wrote: |
| I like to run a slightly shorter belt, that way the belt sits lower in the pulley and the fan spins a bit faster. |
I run the recommended size and drive appropriately. |
Sorry, I have a 5 speed so doing only 60mph in 5th has the RPMs a bit low. |
"Sorry, i have a 5 speed" well ta-ti-da to you. |
Yup, life sux.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare
עַם יִשְׂרָאֵל חַי |
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radbug69
Samba Member
Joined: June 11, 2020
Posts: 199
Location: Maine, North East USA...
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| Posted: Thu Aug 14, 2025 5:08 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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| Cusser wrote: |
I'd start with 5 shims, and go from there. I'm an outlier on this subject as I have intentionally run my generator belts a little looser than specifications on both my 1970 and my 1971, to save wear and tear on generator bearings.
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Gotcha, makes perfect sense regarding saving wear on the bearings.
So, this method doesn't maintain the 5/8" deflection of the belt rather a greater measurement of play..?
I'll try the five like the same number that I removed.
Thanks,
Rob |
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DesertSasquatchXploration
Samba Member
Joined: April 16, 2021
Posts: 1060
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| Posted: Thu Aug 14, 2025 5:31 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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| Glenn wrote: |
| I like to run a slightly shorter belt, that way the belt sits lower in the pulley and the fan spins a bit faster. |
This ^^^
I do a shorter belt in the sand dunes and desert trips spring/summer and run a longer one during winter driving and off-roading. |
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ashman40
Samba Member
Joined: February 16, 2007
Posts: 16769
Location: North Florida, USA
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| Posted: Thu Aug 14, 2025 7:52 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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| radbug69 wrote: |
| ... I removed the old (belt) and made a note of the number of shims, five behind the outer pulley half... |
How many shims were between the two pulley halves?
You want a total of 8 to 10 shims between the pulley cone washer and the inner pulley half. This is to make sure the nut never tightens down to the point where it bottoms out on the shaft threads. The combination of the shims make for a variable sized split spacer that maintains the proper distance so the nut remains over the threaded portion of the shaft.
A common mistake is to change the number of shims between the pulley halves to adjust the belt tension but instead of moving the shims to the other side of the outer pulley you put them in your tool box. This will allow the nut to snug down further on the threads of the shaft and if you remove enough shims the nut will bottom out on the threads. Keep no less than 8 shims on the stack of components between the nut and the generator/alternator.
_________________
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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runamoc
Samba Member
Joined: June 19, 2006
Posts: 6408
Location: 37.5N 77.1W
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| Posted: Fri Aug 15, 2025 5:39 am Post subject: Re: Generator belt adjustment shims, starting point...? |
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with a hi-revving engine, the fan belt will get too tight from centrifugal forces and cause the gen/alt pulley to flex and break and cut a groove on the front of an alt. I adjust from too loose to just tight enough not to slip and don't go by 'deflection'.
_________________
Daily driver: '69 Baja owned 45 yrs - Plan B: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs- '80 Rabbit Diesel
VW Wiring = It's just wires |
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jinx758
Samba Member
Joined: October 04, 2014
Posts: 1047
Location: half a bubble from plumb
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| Posted: Fri Aug 15, 2025 6:10 am Post subject: Re: Generator belt adjustment shims, starting point...? |
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"just tight enough not to slip"
What is that measurement & how do you know when you have reached it ?
I'm not being snarky or confrontational ...
If I can learn/improve I actually enjoy life
My cruddy bug only came with/has 5 shims.
A new belt gets half inch deflection & I always spin the alternator pulley between nut tightening.
It always jumps around at highway RPM but has never flew off, & I drive the snot out it. Both pulleys are in alignment.
I don't baby it at all & routinely flog it just for grins.
I've also never used the belt to advance the crank pulley for valve adjustments.
Trying to learn new skills ... stay safe
jinx
_________________
" It's not valuable unless you learn something from an experience. " Henry Ford
It's not unlike the same difference ...
My Craigslist rescued 100 footer :
1971 Standard Bug
1776cc dual port
034 distributor
38mm EGAS Carburetor |
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radbug69
Samba Member
Joined: June 11, 2020
Posts: 199
Location: Maine, North East USA...
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| Posted: Fri Aug 15, 2025 6:15 am Post subject: Re: Generator belt adjustment shims, starting point...? |
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| ashman40 wrote: |
| radbug69 wrote: |
| ... I removed the old (belt) and made a note of the number of shims, five behind the outer pulley half... |
How many shims were between the two pulley halves?
You want a total of 8 to 10 shims between the pulley cone washer and the inner pulley half. This is to make sure the nut never tightens down to the point where it bottoms out on the shaft threads. The combination of the shims make for a variable sized split spacer that maintains the proper distance so the nut remains over the threaded portion of the shaft.
Keep no less than 8 shims on the stack of components between the nut and the generator/alternator. |
There were five shims in the assembly between the pulley halves...
And good point regarding he total number of shims, the T/M states keeping the unused shims on the shaft although it does not mention the reason that you do about maintaining distance from bottoming out on the shaft threads.
Thanks
| runamoc wrote: |
I adjust from too loose to just tight enough not to slip and don't go by 'deflection'.
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Copy that,
Thanks,
Rob |
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baldessariclan
Samba Member
Joined: October 14, 2016
Posts: 2186
Location: Wichita, KS
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| Posted: Fri Aug 15, 2025 7:14 am Post subject: Re: Generator belt adjustment shims, starting point...? |
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| jinx758 wrote: |
| My cruddy bug only came with/has 5 shims. |
Recommend sourcing some extra shims from used parts vendors or Samba classifieds -- you'll more likely than not be glad you have them available, e.g. when the time comes for a new belt that ends up not fitting quite the same as the old one...
| jinx758 wrote: |
| I've also never used the belt to advance the crank pulley for valve adjustments. |
I find that it's generally easier and more handy to turn the engine over using the generator pulley nut, as opposed to the crank pulley nut. If the belt slips while doing so, you can just push it in a little to tighten while turning -- easy-peasy. Stock generator pulley nut is 13/16", and uses the same wrench/socket as the spark plugs and oil pan plug.
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1971 Standard Beetle — fairly stock / driver
baldessariclan -- often in error, never in doubt... |
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ashman40
Samba Member
Joined: February 16, 2007
Posts: 16769
Location: North Florida, USA
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| Posted: Fri Aug 15, 2025 9:22 am Post subject: Re: Generator belt adjustment shims, starting point...? |
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| jinx758 wrote: |
| My cruddy bug only came with/has 5 shims. |
There are tolerance differences in the aftermarket parts which include the pulley halves and the cone washer and nut. If you want to see if you have enough shims to do the job....
Remove the fan belt, cone washer and nut from the generator/alternator.
If you have an open ended nut, thread the nut onto the shaft until it bottoms out. Measure how much of the threaded portion of the shaft extends beyond the nut. If your nut tightens down to expose this amount of threaded shaft you know you have bottomed out the nut. This won't help you if you have an aftermarket cap nut where you can't see the threads.
Remove the nut and stack all the components in place on the generator shaft, except for the nut. Leave the nut off so you can see how much thread is exposed above the cone washer.
Press down on the cone washer and note how much of the threaded end of the shaft is exposed. At a minimum you want to see at least the thickness of your pulley nut exposed past the cone washer. This will allow all threads of the nut to grab onto the shaft for max retention. Any amount of threads more than the thickness of the nut is unnecessary (unless your threads are damaged).
If you press down on the cone washer and you can see the unthreaded portion of the shaft... you need more shims! More shims will push the cone washer out so the nut rides further out and is no where close to bottoming out. Expect that once your tighten the nut the stack will compress some. Add shims to allow for this.
The only time you would remove shims is if there wasn't enough threads exposed to get full engagement bewteen the nut and the shaft.
The stock nut is rather thin and you only needs 3 to 5 threads exposed to get the nut fully onto the shaft. Aftermarket nuts may have more threads than this but may be of lesser quality. More thread engagement is better, but you never want to see the unthreaded portion extend above the cone washer as this would allow the nut to bottom out.
Someone might be asking, "What about the fan belt? Doesn't this effect where the nut is on the shaft?" The answer is, NO.
You always tighten the pulley nut to the same torque and the stack of components is fully compressed. The count of stack components remains the same so the nut rides the same position on the threads regardless of where the shims are located.
A new belt may be harder to install and get the nut to start threading onto the shaft, but once tightened down fully there is no gaps between the stack of components. It is the same as when you tighten the nut down without the belt installed. So the belt should not make a difference in the location of the nut on the shaft.
The pulley halves are NOT pinching the belt (or they shouldn't be). As you tighten the pulley nut you need to rotate the pulley so the belt rides further out until it finds its proper radius in the groove and the nut is fully tightend. If the belt is too taught, move shims inbetween the pulley halves so the halves are further apart and the belt rides lower in the groove. If it is too loose you move shims out from the halves which cause the same belt to ride further out inbetween the pulley halves and tightens the belt tension. In all cases the total count of stack components remains the same so the nut tightens down to the same point along the threads. If this is not happening, you are doing something wrong.
_________________
AshMan40
---------------------------
'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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runamoc
Samba Member
Joined: June 19, 2006
Posts: 6408
Location: 37.5N 77.1W
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| Posted: Fri Aug 15, 2025 9:38 am Post subject: Re: Generator belt adjustment shims, starting point...? |
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| Quote: |
"just tight enough not to slip"
What is that measurement & how do you know when you have reached it ? |
As I'm tightening the gen/alt nut and the pulley slips, I take out another shim. Not tight enough to actual turn the engine over, just move it some. Since doing it this way I haven't broke any gen/alt pulleys or cut a groove in the front of my alt and the battery charges.
_________________
Daily driver: '69 Baja owned 45 yrs - Plan B: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs- '80 Rabbit Diesel
VW Wiring = It's just wires |
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jinx758
Samba Member
Joined: October 04, 2014
Posts: 1047
Location: half a bubble from plumb
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| Posted: Fri Aug 15, 2025 10:13 am Post subject: Re: Generator belt adjustment shims, starting point...? |
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Kool beans ... thanks much for explanation of procedure !
Definitely gonna get more shims - I have a semi-local source for some OE quality stuff.
I should replace my belt as well. It is at least 8yrs old but has no glazing, cracks, or separating anywhere.
Yay - I get to do something besides turn the key & drive !
(I know I need help, it's not safe in here ! - - points to forehead while twisting wrist).
Been putting off R&Ring the oil cooler seals, too.
Now about that 103* weather + 85% humidity ...
: (
Best to all ... stay safe
jinx
_________________
" It's not valuable unless you learn something from an experience. " Henry Ford
It's not unlike the same difference ...
My Craigslist rescued 100 footer :
1971 Standard Bug
1776cc dual port
034 distributor
38mm EGAS Carburetor |
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radbug69
Samba Member
Joined: June 11, 2020
Posts: 199
Location: Maine, North East USA...
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| Posted: Fri Aug 15, 2025 5:53 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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Well, that belt change is a strange procedure...
One thing that I could not help from notice that the shims are different than the ones I removed. The five that were in the assembly were .020", the replacements are right at .028".
At any rate, the belt seemed a bit tight after installed, not too tight, just more taut, perhaps that it is new, I'll keep a close watch on it.
On to the Regulator in the AM... |
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Glenn
Mr. 010
Joined: December 25, 2001
Posts: 80418
Location: Sneaking up behind you
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| Posted: Fri Aug 15, 2025 6:01 pm Post subject: Re: Generator belt adjustment shims, starting point...? |
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Are the old ones OEM and the new ones aftermarket?
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare
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