Can't change HingeJoint properties by script

I have this script attached on a gameobject with a Hinge Joint. When click up/down, the value is changed. The debug shows the new value, but nothing happens on Inspector and gameobject still doesn't move. If I put same values by inspector, works. What to do?

 public class Mover : MonoBehaviour
 {
     JointMotor motor;
 
     void Start()
     {
         motor = GetComponent<HingeJoint>().motor;
         motor.targetVelocity = 5;
     }
 
     void Update()
     {
         if (Input.GetKeyDown(KeyCode.UpArrow))
             motor.force += 2f;
         else if (Input.GetKeyDown(KeyCode.DownArrow))
             motor.force -= 2f;
 
         Debug.Log("Force:" + motor.force);
         Debug.Log("Vel:" + motor.targetVelocity);
     }
 }