That is right but it is a dynamic balance item, as opposed to the more
simple static balance. Dynamic balance is why it makes a difference
whether they put the weights on the inside or outside of a wheel on
your car (or some on both). If both the engine without the pulley
and the pulley itself were in balance it shouldn't make a difference,
so that it sounds like maybe the pulley itself is out of balance.
It could also be a fan imbalance. They are fairly heavy and turn fast.
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George Downs, Bartlesville, Oklahoma, Central US