What Crank Pulley are you running? Sounds like something is not right there.
ABA pulley must be properly shaved and centered 5.8mm for use on a 16v/20v
I did this swap, AEB into my MKII GTI, it hums, it's fast, it's light and still corners really well super happy with it!!! Great decision. I run ABA hardware on the engine, and put a spacer inbetween the pully that doesn't quite allign properly... here's where it gets tricky. I have this all done, but now i'm shredding belts after driving for a few days, and i think it's because the tensioner isn't alligned properly. I can't remember off the top of my head the size of the belts I'm using, but i know that i had to switch to a longer length by a mm just to get the belt on after i shredded the first one. I think that belt was too tight and ruined the alignment of my tensioner, but now i have a whole new problem and turning to the advice of those who've come before me. Anyone run into this problem before or have any advice???
You can use a modified Bahn Brenner crank pulley typically meant for 16v swaps. That's what I used on my AEB swap running ABA bracket, tensioner, and alternator.
The nice thing about the BBM pulley is that they machine it to fit a locating ring in the center. This keeps the pulley true to the crank and free of vibration.