The deformation of the split surface of the head is checked with a gauge and a feeler gauge diagonally and along the head along the center line in several places (photo). If the deviation from the plane exceeds 0.076 mm in a section of 152 mm, or 0.152 mm along the entire length of the head, then the head should be reground. If the head of the V6 engine is being ground, then the plane of the intake manifold should also be ground and the manifold adjusted in place for its correct installation.