The non-flatness is eliminated by grinding the mating surface of the head on the CTOA, for this it is necessary to check the height of the cylinder head. The nominal height of the cylinder head is 140.0 mm, the minimum permissible, after grinding, should not be less than 139.7 mm. Under the cylinder head that has undergone grinding, it is necessary to install a repair sealing gasket of the cylinder head, which is 0.3 mm thicker than the standard one and has the index "+0.3" in the marking (Fig. 3.73).
Before installation, the cylinder head must be checked for leaks using a set of devices for its sealing. Connect a source of compressed air to the device and immerse the cylinder head in a bath of water; if necessary, you can reduce the hardness of the water with detergents. Apply a test pressure of 4.5 bar (kgf/cm²) and check the tightness of the cylinder head for cracks in the walls by the appearance of air bubbles.
(This article is based on information from the website: «BMWMan»)