The oldest method of straightening alloy heads requires the cylinder head to be controlled heated to around 260c to 300c., while having the bend removed by press or clamping plate. This method requires a considerable amount of over straightening to allow for spring back when the pressure and temperature are back to normal. This method is not very successful and can damage some heads beyond repair. Often a cylinder head will break in half rendering it useless. As this method requires the head to be heated above what is recommended by the manufacturer some softening of the head can occur.
An alternate method was developed that does not require so much over bending of the cylinder head and only requires the head to be heated enough to take the chill out of the casting. This methods requires the head to be bent just a few thousand's of an inch over straight and to be held in that position while selected positions of the upper tappet cover area of the head are spot heated. The localised melting of these small areas act as locks to hold the head straight. The main advantage is the low heat applied to the head does not cause any change to the hardness of the head. This method requires less over bend as the selected areas heated cool down to form physical locks to hold the head straight.