Rotor trim balancing

A construction for trim balancing a rotating piece of machinery, said machinery including an annular rotor element having an outer face and an inner circumference, a series of locating slots about the inner circumference of said rotor element, two annular grooves within said rotor element behind said rotor element face, balance ring means in each of said two annular grooves, beach balance ring being split and having a weighted mass at one end thereof and tab means connected by pin means to the balance ring at said weighted mass end, said pin means extending through said rotor element locating slots and said tab means being mounted on said pin means so as to be external of said rotor element, said machinery also including casing structure means associated with said rotor element, said casing structure means having an opening therein through which tool means may be inserted to contact said tab means and deflect said tab pin means inward a controlled distance to release said tab pin means from the locating slots and permit a circumferential relocating of said balance ring means, said tab means having a surface contoured for contact by said tool means.