Heavy sparking at brushes indicates shorted armature or short in field. Examine commutator bars, should look dark gray to black but very smooth. If scratched or pitted most likely end of life. If not too bad could be weak brush springs or worn brushes. Brushes should be at least 1/2 to 3/4 in in length. If commutator and brushes good , suspect field. Good luck
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Heavy sparking at brushes indicates shorted armature or short in field. Examine commutator bars, should look dark gray to black but very smooth. If scratched or pitted most likely end of life. If not too bad could be weak brush springs or worn brushes. Brushes should be at least 1/2 to 3/4 in in length. If commutator and brushes good , suspect field. Good luck