belt throwing

Hi Guys,

i have a mixed set of pulley on my engine, don´t even know where these are from originally. The alignment is good, but it keeps throwing the belt over 5000 rpm....no fun at all.

the lower pulley does not run perfectly, it has got a slight "shake", don´t exactly know how to explain. the belt is around 47" long.

can this cause the problem? How long is the water pump / alternator belt originally?

Michael