My Robotics team can’t find if it is competition legal to modify Vex 393 Motors in the Vex rule’s. We want to take out the PTC in the motor since our motors are getting hot and the PTC turns off the motor.

It is illegal. Teams that are caught with modified motors can be disqualified from a competition. At the larger events robots will be checked for modified motors during inspection.

Here is a post from the head of the GDC explaining this position.