While other Audi A4 engines operate with roller rocker arms, the 1.8L turbocharged engine (AVJ) has hydraulic tappets. Therefore, drivers of some Audi vehicles may also encounter a situation where a tappet malfunction manifests itself as noise in the valves. Knocking may also occur due to faulty hydraulic tappets, this occurs 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 period of inactivity.
- The car had 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 the noise in the valves disappears after a long drive, but appears again at the beginning of the next trip, then the oil check valves need to be replaced.
In order to replace a faulty tappet, which should always be done as a set, you need to remove the camshaft. This is a job for a workshop. On the contrary, you can check the hydraulic tappet yourself. To do this, you need a feeler gauge to check the gaps, as well as a wooden or plastic wedge. However, to get to the hydraulic tappets, you first need to remove the cylinder head cover, under this cover are the camshafts.
The working principle of a hydraulic tappet
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 be changed. This allows for compensation of different clearance sizes.
When the valve is closed, the pressure between the two oil chambers is equalized. The piston spring pushes the piston upward, there is no gap between the cam and the rocker arm. When the cam runs onto the rocker arm, the piston is pushed downward. As a result, high oil pressure is created in the lower chamber. Due to this high pressure and the force of the spring, the ball is pushed upward, 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 compensation element acts as a stationary part on which the rocker arm rests. The force of the cam can be transmitted to the valve, and the valve opens. When the cam comes off the rocker arm, the ball again opens the passage between the two chambers, and the pressure is equalized.
[Read the original source on the website AudiManual.ru]