Series DC Motor brush advance

Part one of my first experiment with advancing the brushes of my 13" forklift motor made by pyroban and rated at 80v. Any advice most welcome!

Part two of my first experiment with advancing the brushes of my 13" forklift motor made by pyroban and rated at 80v. Any advice most welcome!

Part three of my first experiment with advancing the brushes of my 13" forklift motor made by pyroban and rated at 80v. Any advice most welcome!

Part four of my first experiment with advancing the brushes of my 13" forklift motor made by pyroban and rated at 80v. Any advice most welcome!