The grinding of the surface of the cylinder head, or flattening of the cylinder head, is a very important step, but not all the cylinder heads can be flattened, at most the surface can be rectified by a few hundredths of a millimeter.
Some engine heads may have been deformed due to overheating and / or lack of cooling, this problem causes the surface to bend, causing the engine gasket to burn.
The engine head leveling machine is a tool-based machine that smooths the surface by removing the minimum material necessary to bring the head surface perfectly flat and smooth with the right polishing or roughness.
Today many workshops disassemble the head without checking the plan, but only cleaning it. It is absolutely necessary to check the flatness with a special groove and if necessary to smooth the surface maybe only a little, because today’s heads are tightened to such high forces, that just disassembling them cause surface deformations that would not guarantee the seal between the engine block plane., cylinder head gasket and cylinder head.