You can do a search "Blower Oil"
Most of the motors have little holes on each of end, that you can put some drops of good Electric Motor Oil (I think SAE 20). Sometimes the motors have to be removed, the holes may end up on the bottom of the housing. If they don't have the small holes/tubes, then probably sealed bearings, not much you can do except when they start making noise, replace them.
Here a thread with a picture.Blower fan?