The cylinder head is assembled in the reverse order of disassembly, taking into account the following:
- before installing the valves, lubricate the holes in the valve guides and the valve stems with engine oil;
- before pressing the valve stem seals onto the valve guides, tape the valve stem seal grooves to protect the valve stem sealing edges from damage;
- valve springs are of the progressive rate type. Install the springs so that the most compressed coils of the spring are (with color marking) rested on the cylinder head;
- install the upper spring plates and valve crackers, compressing the springs by installing the pressure frame (see subsection "Disassembling the cylinder head") or a universal device for removing valve springs;
- insert the rocker shafts, paying attention to the correct position of the springs, rocker arms, support and mounting washers (see photo). On models "518" and "520" pay attention to the fact that the hole in the shaft of the intake valve rockers on the side of the rear end of the cylinder head remains open, and the hole in the shaft of the exhaust valve rockers on the same side is closed with a plug (see photo). If the plug does not fit tightly, it must be replaced; when installing a new plug, apply a sealant such as Loctite AVX to the mating surfaces;
- on models "525" and "528" before installing the rocker arm oil distribution channel plugs, lubricate them with a sealant such as Loctile No.73;
- when installing the valve stem axles, it is necessary to align the recesses in the axles with the holes for the cylinder head mounting bolts;
- install guide pins to prevent deformation of the rocker arm axles (see photo);
- install the pressure frame on the cylinder head, install the camshaft, making sure that the valve clearance adjustment eccentrics on the rocker arms are in the position corresponding to the maximum clearance, and lubricating the bearing journals and camshaft supports with engine oil.
- install the protective cover and the bracket of the ignition distributor, replacing the sealing gaskets (use only "Cobritol" type gaskets) and installing the saved sealing washer 1 (see photo);
- direct the central oil supply tube so that the oil jets hit the rocker arm axles.
(You can read the original on the website: BMWMAN.ru)