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Discussion Starter · #1 ·
I have some strange goings on with pulley belts which is really causing me confusion and starting to be a bit of a pain in the arse.

1641TP engine. Billet aluminium alternator pulley, aluminium crank pulley with degree markings.

After about 20,000 km on this engine the alternator belt started to squeal so I adjusted it. Almost immeditely it started squealing again, so I adjusted it even further. Over time this has been happening more frequently. It's like my engine is shrinking in height.

I'm now at the stage where a brand new belt (Optibelt 11.3 x 912) is a little bit loose even without any shims between the pulley halves. In my spares that I carry with me I have about 6 or 7 belts all of which are practically new but all too big to be useful on this engine.

I have recently undone the alternator strap and checked that the alternator is secured as it should be, which it seems to be. I have noticed however that the alternator strap is tightened up to the maximum that it will allow (which I have also noted on other aircooled engines, not just mine) - it's as if the alternator strap should've been made 10mm shorter. I am satisfied that the alternator is secured tightly and doesn't move. The alternator sits on a stock generator/alternator stand.

Recently, I cut a piece of tin from a can of tuna and stuck this between the alternator and it's stand - effectively raising the alternator slightly. This worked for a while but within 1000km the belt started squealing again.

I know some will say that I should bin both pulleys and replace with stock items but that would suggest that everyone running these aftermarket items would be having the same problems, and I don't buy that.

Where am I going wrong? This must have something to do with the position of the alternator, no? :confused:
 

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I've never had a prob with an Ali bottom pulley but had a few probs with cheap steel top ones. Main issues for me were with them twisting and rounding off the centres or cutting slots on the 2 tabs than they go rattly and come loose. I'm supprised an Ali pulley is up to the job for that reason, are you sure it's just not excessive wear as the belt cuts it's way down the groove?

Could be it's not aligned causing the belt the climb and stretch over time?

Not going to like this answer but going back to a ge uine stock pulley sorted my issues out with aftermarket parts. Sorry.
(Coukd always look at having it chromed or Nickel plating it at home etc?)
 

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Seriously, just replace the pulleys. I had aftermarket pulleys, they ended up in the bin.
 

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I know some will say that I should bin both pulleys and replace with stock items but that would suggest that everyone running these aftermarket items would be having the same problems, and I don't buy that.
Think you might have answered your own question.... ^^^^

But assuming both pulleys are tight on their shafts, and that the alt bearings are not on their way out, and the alt is fully bolted down, and the alt stand is not warped or cracked, then it's probably the soft aluminium wearing down making the pulleys effectively larger diameter.

Of course once you have a loose belt and it starts to slip it's rubbing the soft ali and will wear a groove.

However people running an ali bottom pulley & steel top one won't have this problem very much as almost all the slippage is going to occur at the smaller top pulley as that has less grip on the belt. And by the sounds of things you're probably doing a much higher mileage than the vast majority of other ali top pulley owners.

Got access to a lathe ? Skim .5mm off the inside mating face of the top pulley and see if you can get good belt tension with 4 or 5 shims to give you some breathing room for the next 20K.

Dave.
 

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I have just read an article on the samba about billet top pulleys as i was thinking of getting one, one person had similar problems but he couldnt tighten it enough i think it depends on make and quality, again i have never had a problem with alloy bottom pulleys and have always used standard orignal top pulleys.
 

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Replace the pulleys before you damage your engine. VW were fanatical about weight saving on the Beetle (hence the extensive use of magnesium) so ask yourself why they did not use aluminium for the pulleys...
 

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Discussion Starter · #7 ·
Seriously, just replace the pulleys. I had aftermarket pulleys, they ended up in the bin.
Hi All. Soz for not responding sooner. Those that suggested replacing the pulley for a stock item were right. The billet pulley fitted to my new build engine lasted 16000km before it has worn to the extent that you couldn't adjust the belt any further. As they say, Chrome don't get you home. And don't buy billet pullies. Thanks guys for the suggestions.
 

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There is also a problem with the quality of new belts, they stretch for fun. As has been said replace the pulleys to eliminate them as the cause of the issue.
 

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There is also a problem with the quality of new belts, they stretch for fun. As has been said replace the pulleys to eliminate them as the cause if the issue.
I've had new belts stretch within a few hundred miles to the point theres no adjustment left. Continental ones not no brand chinese ones too.
 
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