This is hard work! How are they 'modified'? What do you mean when you say they don't do the job right? What exactly are they doing instead?
Just some background information: if you want the motors to rotate exactly five times, you have basically two ways of doing it. You can use stepper motors and send enough pulses for five rotations. Or you can use normal DC motors fitted with a position sensor (such as a flag and an optical sensor) so you can count five rotations and then stop the motors.