Insert BMW special tool 11 4 430 or equivalent sealing plugs into bore holes and remove coarse residues on sealing surfaces from the cylinder head and crankcase, taking care not to use metal-cutting tools to avoid damage. Use BMW special tool 11 4 472 or equivalent grindstone to remove fine residues, ensuring all blind holes are cleaned to eliminate coolant, water, or engine oil to prevent cracking or corrosion. Inspect the cylinder head for visible cracks or defects, and check for warpage by removing intake and exhaust camshafts, roller cam followers, valve lifters, and valves. Use a straight edge to assess the evenness of the sealing surface in both longitudinal and transverse directions, and have the cylinder head tested for coolant leaks and cracks. If warped but sound, machine a maximum of 0.3 mm (0.011 in) off the sealing surface, then reassemble or use a reconditioned BMW cylinder head, ensuring it is placed on its side to avoid valve damage. Replace the cylinder head gasket with a special one from an authorized BMW dealer if machined, as it is 0.3 mm (0.011 in) thicker than standard. Position the cylinder head on the engine block, fitting it to the aligning sleeves, and install new cylinder head bolts using the appropriate BMW special tools. Retrieve the timing chain from the housing, place it over the chain module, and reattach the module with new bolts, noting the differences between exhaust and intake camshaft adjustment units. Lock down the camshafts with the specified tools, install the chain tensioner, and set the camshaft timing. If reusing the chain tensioner, drain its oil chamber and compress it slowly. Ensure a new sealing O-ring is used during reassembly. The remainder of the installation follows the reverse order of removal, including removing locking tools, assembling the cylinder head cover with a new gasket, reattaching ground cables, reinstalling the engine, adding fresh engine oil, checking the oil level, and filling and bleeding the cooling system.