[Lynn Eades]

I do not believe bead blasting would do any harm what so ever to your gears. You are talking glass beads, I assume. The stuff is however, harmful to your lungs, if you don't take the pecautions required. It is also very important that your clean up of your parts (to have them 110% clear of any glass residue) is vitally important.
Glass bead blasting can make a component more durable because it tends to eliminate stress points from which fractures start.