i have an electric motor. when i put the two screws on to hold the head piece down it wont work, but when they are not on it works. what is the problem??????????

If you have replaced those two screws, it is possible the new ones are too long, allowing them to actually hit/catch on the armature segments...?

I am assuming that when you say "head piece", you are talking about the endbell, with the brushes, springs, etc.... right?

where it attachs to the car or what he said if so they are to long either way