You may need to resurface your cylinder heads to improve the finish of the surface, restore flatness to the head. After welds or other repairs have been done to the cylinder head such as increasing the compression ration, the cylinder head may need resurfacing. Regardless of why you need to resurface the head, the important part of the process is getting it done quickly and correctly. If you make a mistake, it can cost you. You can not remove too much metal because you can not put back what has been taken away, resulting in having to purchase a new cylinder head.