Motor pulley was changed to a non keyed hub,Motor was changed to a keyed shaft,Maybe the comp pump is trying to lock up,pulley never had a keyway and just used the set screws. Lot of 'options' here .
Pull the pulley off and see if it originally had 2 set screw 'marks' elsewhere on the motor shaft.
Tightening the set screws INTO the motor KEYWAY is A VERY BAD THING. You likely with have a hard time removing the pulley as you created an interference fit by gouging the shaft and unfortunatly,the pulley is up against the motor bellhousing and only one way to get off. If you try to pry the pulley using the motor as a pry block, be careful to not damage the motor bearings or endbell.
Your at a point where you need to remove the whole motor/pulley assembly and really find out the problem and room to work in.