A process for renewing a cylinder head, preferably a cast aluminum water cooled cylinder head from a used condition to a rebuilt condition suitable for reuse. In a qualifying stage the used cylinder head is stripped of removable parts, inspected, heat treated for cleaning and stress relieving purposes, and then pressure tested to detect leaks through cracks or excessive porosity. If cracks are located, the cylinder head passes through a reconstruction stage wherein cracked areas are removed and replaced by welded material, recontoured and preferably again pressure tested. A cylinder head which did not need reconstruction (or after reconstruction) then passes to the rebuilding stage where it is essentially machined and component parts replaced. Included in the rebuilding stage is a line-boring and surface gasket facing procedure for eliminating the adverse effects of warpage and a vacuum impregnation step to seal the pores of the cylinder head.