The cause of a malfunction of the starter components can be:
- excessive wear of carbon brushes and springs;
- high resistance due to severe contamination of the collector;
- short circuit in the winding;
- a bad bearing that causes the rotor to rub against the poles.
Check the spring retainers and starter carbon brushes for wear.
Check the starter manifold for dirt.
Check for play in the starter bearing.
If the listed malfunctions could not be found, replace the starter.