Hmmm,
a warm engine is harder to turn than a cold engine.
Probably the engine heat warms up the starter motor and eases its job ?
First thing to do is to clean the collector and to fit new brushes/coals[?].
Also clean the gaps of the collector with a small tool. Soft material (plastic) is prefered over metal objects.
To disconnect the PLUS-cable, ensure the internal screw/stud doesn’t turn. If it does more than approx 30° the internal copper strips will brake off (last pic) !
Use a simple, but flat 10mm spanner to hold it, e.g. available from bicycle dealers as universal tools for just 1 pound.
Never disassamble the 4 screws circular to the housing !
For reassambling of the starter motor the alternator cover must be off.
Pay a lot of attention to the washers and their sequence !!!
You can’t remove the rotor to the Brush/coal side. Just leave it in the housing to clean the collector.
Cheers, Michael
PS: I describe this brushes/coal side as the electrical side of the starter motor.
The other side is the mechanical side. It is more complex and not straight-forward to reinstall.
Pay even more attention to the washers there ! One sticks always at the rotor, make sure to catch that.
