It is possible to have pre war and post war model train motors for many brands of model trains (like Lionel, American Flyer and Ives), rebuild and made to run like new. However, the armature core needs to be intact for an experienced repairer to do the job successfully.

A sign that one of the armature coils may be open circuited is when the brushes on a model train give off a lot of sparks.

A model train motor may need an armature rewind when the motor runs very hot and slows down after a just few minutes of operation.

A tell-tale sign that the armature has been damaged is when the armature wires look dark in color relative to the other windings on the armature.

Another sign that the armature has a problem is when the field winding over-heats. This could be an indication that the current flowing through the series circuit made by the field and the armature has a very low resistance.