We suggest removing factory grease one of two ways. The first is to run them in an ultrasonic cleaner for 30-60 minutes and spin test. Repeat if bearings do not spin satisfactorily. The second is more involved. Remove the shields and run them in an ultrasonic cleaner for 10-15 minutes and all grease should be removed. Our preferred solvent for this procedure is denatured alcohol as it removes everything without leaving any residue behind.