Why Even Perfectly Balanced Machines Start Shaking Once They Warm Up By Josh Iris, President, Ace Electric Motor & Pump Co. If you’ve been around rotating equipment long enough, you’ve probably seen this one. You rebuild a motor, line it up perfectly, and balance the rotor to G 1.0. It runs smooth as glass at startup. But ten minutes later, the vibration starts creeping up. You double-check everything — balance, runout, coupling, base — all good. You pull the laser out again