With DC motors you can reverse line leads all day and they will not reverse. You must reverse either the field or the armature circuit to get reversal.

The older motors more than likely have a wound field so you have to reverse it or the armature. If you have only two wires coming out of motor you cannot do as is. YOu will have ot open up and bring out both the armature and field leads.

The China motors are more than likely permanent magnet. In this case reversal of line leads reverses just the armature which is why they reverse.

Dan Bentler