Spiral balance keeps popping out of pivot shoe

I wonder if you need to charge the spiral balance spring. With the window sash removed from the master window frame, raise the spiral up to the balance tube and give it three turns (it is easier with the charging tool #75-006, but you can try it with needle nose locking pliers) and lock it in the pivot shoe. Then reinstall you sash. If this does not work or you did not feel tension when you charge the balance, then you need a new balance.

A few other things to check for.

Make sure you are charging up the balance in the correct direction. (you will feel the tension in the spring when you are charging it).

Install the spiral in the correct slot in the pivot lock shoe. It should be installed either in the left slot or right slot depending which side of the window you are facing.