2. Increase the speed for two minutes to 2500 rpm. If necessary, carry out a test drive. If the irregular valve noise disappears and reappears at the beginning of the next drive, it is necessary to replace the oil relief valve in the oil filter holder. If the hydraulic disc tappets still make unusually loud noises, then in order to determine the defective tappet (defective tappets), do the following:
3. With the cylinder head cover removed, turn the engine, i.e. rotate the crankshaft clockwise until the cam of the plate tappet being checked is facing up. In the case of a car with a manual transmission, the engine can be turned by pushing the car forward with the fourth gear engaged and the ignition off. In a car with an automatic transmission, you need to remove the soundproofing cover and rotate the crankshaft clockwise using the central bolt of the crankshaft gear.
4. Determine the clearance between the cam and the tappet. If the clearance exceeds 0.20 mm, the tappet must be replaced. Using a wooden or plastic wedge, press the tappet down (see picture). If a 0.20 mm thick feeler gauge fits between the camshaft and the tappet, the hydraulic tappet needs to be replaced (in the workshop, during which the camshafts and camshaft adjuster are removed and reinstalled).
With a wooden or plastic wedge, press in the direction of the arrow
5. After installing the camshafts with new plate tappets, the engine must not be started for about 30 minutes. The compensating elements must be installed first, otherwise the valves will sit on the piston. After completing the work on the valve train, carefully turn the engine at least two revolutions. This ensures that no valve sits on the piston when the engine is started.
[The text is based on materials from the website: AUDImanual.ru]