Need help for a friends car.
 

I have a friend who drives a 2000 Jetta VR6 with the 2.8 litre motor. It was being driven when it threw a belt. After I finally figured out how to work the tensioner on it I got the belt replaced. When I started the car it promptly threw the belt again and I thought I had mis aligned it, while trying to get it back on track I found the Smooth pully on the left (looking at the motor from the passenger side) to be wobbling back and forth. I tried putting an allen key in the three screws on it and tried to tighten it but got nothing.

My question is, is this a known problem, what is the pully driving, the best course of action to go about fixing or replacing the pulley. I can not see an easy way to stop the pulley from spinning while I try and lossen the bolt holding it on so any tips or trick would be very helpful.


Thank you for any and responses.