While the rest of the Audi A4 engines work with roller rocker arms, in the 1.8 liter turbocharged engine (AVJ) there are hydraulic pushers. Thus, drivers of some Audi vehicles may also experience a situation where a tappet failure manifests itself in the form of valve noise. Faulty hydraulic pushers can also knock, this happens in the following cases:
- Immediately after starting the engine, there is not enough oil in the system. This can happen, first of all, after a long parking.
- The vehicle has previously been subjected to heavy loads at high outside temperatures.
- When the oil level is very low, the oil pump sometimes sucks in air.
If valve noise disappears after a long drive and reappears at the beginning of the next trip, the oil check valves must be replaced.
In order to change a faulty pusher, and this should always be done as a set, it is necessary to remove the camshaft. This is workshop work. On the contrary, you can check the hydraulic pusher yourself. This requires a feeler gauge and a wooden or plastic wedge. True, to get to the hydraulic tappets, you first need to remove the cylinder head cover, under this cover are the camshafts.
The principle of operation of the hydraulic pusher
The hydraulic tappet is connected to the engine oil circulation system. The amount of oil in the lower chamber on which the piston rests can vary. This allows you to compensate for the gap of various sizes.
When the valve is closed, the pressure between the two oil chambers is equalized. The piston spring presses the piston upwards, there is no gap between the cam and the rocker arm. When the cam runs onto the rocker, the piston is pressed down. As a result, a high oil pressure is created in the lower chamber. Due to this high pressure and spring force, the ball is pressed upwards, the ball closes the passage between the upper and lower oil chambers. Thus, the piston rests on the created hydraulic cushion of the lower oil chamber. The valve clearance compensating element acts as a fixed part on which the rocker arm rests. The force of the cam can be transferred to the valve and the valve opens. When the cam comes off the rocker, the ball again opens the passage between both chambers, and the pressure equalizes.
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