engine idle; crank shaft pulley rotating but belt won't turn with it

thank you for your response daveJHM. my answer to your question is yes and yes. its like there are 2 rotating pulley cascade together. the internal pulley rotates but the external pulley does not. thats how i can best describe it by looking at the engine while it is in idle.

If I am not misaken, it's the pulley itself that requires replacement. It should be a dampner assembly - that is, connected by rubber to dampen engine vibration. The rubber may have torn, causing the pulley separation.

if i am going to buy this part, how do you call this part? crank shaft pulley assembly?

it looks like this http://www.napaonline.com/Search/Detail.aspx?A=BK_6002485_0259269156&An=599001+101999+50026+2026029#

Pretty much, but I would probably defer to a dealer part, just for overall part quality, longevity and fitment for something like that.