replaced my bent top pulley with a new one and couldn't get the fanbelt tight enough,so got a shorter belt,then found after a short time its loose again : got no shims to take out and its a bit loose,got an altenator belt..
these are good ,fitted one recently to my bus with no issues http://www.coolairvw.co.uk/Item/NA/AC903113/12V_Dynamo_-P-_Alternator_Spin-Tru_Black_Pulley.html
Steer clear of these http://www.machine7.com/product.php?xProd=12919&xSec=188. bag of sh1te. thread wore in the nut and the thing chattered itself to pieces. Didnt get a refund either - long story Tempted to try one of these http://www.bullyspulleys.com/
the one on machine 7 is pretty much the same as the cb performance one, i bought one of them the other year from stateside and the belts never been tight enough in my K'Ghia not sure i wanna go back to stock as it's on view so to speak so looking for something good enough as stock but will actually work!
something my mate said in regards to pulley's was on another msg board which may be of use to some people on here >>> top pulley always needs the shim pack ( theres seven or so, cant remember how many ) and if you have 3 between, then the remainder go behind the nut.... the total width of the shims makes up the effective length thats being clamped ... without the shims.... youll think the nut is tight... BUT its just bottoming out !!! and the 2 pulley halves are just floating free, resulting in the fan belt drifting loose, the pulleys running loose... and a cooked motor or exploding pulleys !