What kind of heads, iron or aluminum?
If aluminum what do the springs sit on? Do the spring seats or cups center and make sure the inner springs don't rub against the valve seals? If not fix that next
The motor is talking to you about it not being happy, now comes the hard, part understanding what is causing the motor to be unhappy and hurting itself
Let us know what you find That may and will probably help others on here later with similar issues like yours