It's about balance and not so much about RPMs, the motor cannot spin faster than it was designed for. If the impeller is caked with ash and starts to corrode, the shaft will wobble...not to mention hair, dirt and other debris all causes the bearings to wear and then the problem gets worse. Most mfg don't do engineering tests to design motors specific to their use and as such, the wear out quicker than say whitfields, which had motors designed especially for them....which everyone copied and started using. I love going to an old whit that's 23+ years and still has all its OEM parts from day one installed.
