In large rotating machinery such as turbine generators, it is common practice to carefully balance the shaft and rotor elements of the generator prior to mounting them in a stator, in order to minimize vibration and whirl during operation. Nonetheless, it is frequently necessary to perform a final balancing of the machine once it has been installed at its location of intended use. To facilitate such final balancing operations, prior art rotating machinery usually includes small, capped inspection openings through which balance weights may be inserted into recesses already machined in the rotor for this purpose. Specifically, it is known to place a balance weight at the end of a long rod which is frequently screwed into the weight. The weight is then inserted into a recess in the rotor and the rod is struck as necessary to upset the material of the balance weight so that it will remain in the recess. In this type of balancing, it is frequently difficult to remove the rod from the weight following the upsetting; moreover, the rod itself is rendered useless fairly rapidly due to the repeated blows required for upsetting the material of the balanced weight.