What level of sparking is acceptable from a YDK motor? I acquired a DC07 recently with an apparently blown motor. I fitted a new after-market motor, but then decided to inspect the old one a bit more closely. It was dead, but powered up OK once new brushes were fitted (the old ones were badly worn down) and the commutator cleaned-it wasn't badly scored. However, there is some 'localised' sparking between brushes and comm visible when bench testing it. Other than that it seems to run OK. Is this acceptable/normal, or is it likely to fail again fairly quickly?
There seem to be two schools of thought as to whether brush changes are worthwhile.