I have a model 673 snow blower on my lawn tractor. I bought it well used. The snow blower keeps throwing the long drive belt and I noticed that the 7" drive pulley on the blower just wobbles around. The bolt holding it on the shaft is tight but the pulley wobbles really bad. Threw the belt 5 times. Is it supposed to wobble? Or is the pulley bad? The belt is tight when on.