BELT TENSIONER.....I really need help here!!!

[TeeJay3800]

While running the engine with the hood open, I noticed that my UD pulley (I mean the wheel spun by the crank) seems to be loose or out of balance. Its almost looks like its out of round. The tensioner is moving up and down real fast and the UD pulley is clearly not spinning in a perfect circle....as it spins, its not smooth at all, like its loose or out of round. The wierd thing is I don't feel anything strange from behind the wheel.

Is the pulley just loose or is it damaged somehow? Is it the pulley itself or something else? Any help is appreciated! Thanks in advance.

EDIT: AFTER LOOKING AT IT CLOSER, THE CRANK PULLEY IS FINE....ITS SEEMS TO BE THE BELT TENSIONER. WHAT WOULD CAUSE THE TENSIONER TO MOVE UP AND DOWN SO MUCH?

[Manitcor]

the tensioner is spring loaded, over time the spring weakens. Its time to replce the tensioner. About $50 for an aftermarket part found at most auto stores.

[ko0t3rskkar]

The belt tensioner will move some. It shouldnt be alot but it will move. Mostly because of the alternator, when you have the alternaotr under load it takes more for the engine to spin it. The crank pulley is pulling one way on the belt and the alternator is pulling the other way. This will make the tensioner jump up a little. Not a whole lot, just a little, if it has more than about 5/8" of travel id say, it may need replacing. Mine jumps up and down like crazy, never have had any trouble with the belt sqealing. Even before I put the new belt on about 5 months ago. The old one was shot, it had grooves missing out of the bottom side, and the top side was shiny as a new quarter. Never had any trouble with that one slipping, but I figured I better replace it since it was falling apart.
And my crank pulley moves a little too. I wouldn't worry about it.