What are hydraulic pushers for?
As the engine heats up, the valve train components stretch and elongate. Therefore, there must be a small gap between the camshaft and the poppet pushers, so that even when the engine is warm, the valves close tightly, despite their slightly longer rods. This clearance, the so-called valve clearance, had to be adjusted at regular intervals in older vehicles. In the Audi-100, this action takes place automatically at each valve cycle due to the so-called hydraulic valve clearance adjustment located in the poppet tappets. Hence the name «hydraulic pushers».
Valve knocks
Knocking noises in the cylinder head area indicate one or more defective hydraulic tappets. However, valve knocking can also occur with fully serviceable hydraulic tappets if:
- the oil supply of the tappets has not yet been ensured - the engine has not warmed up enough.
- the vehicle had recently been operating at full load at high outside temperatures.
- The car has not been used for a long time. In this case, the knocking of the valves should stop at the latest when the engine reaches operating temperature.
- When the oil level is very low, the oil pump sometimes draws in air.
Search for a faulty hydraulic pusher
Start the engine and let it run until the electric cooling fan runs for the first time or, on a 5-cylinder engine, the coolant temperature gauge is over 80°C.
Increase the speed for two minutes to approximately 2500 rpm.
If the knocking does not stop, stop the engine and remove the cylinder head cover.
Set the first cylinder to the TDC of the ignition moment.
Press both poppet tappets next to the first cylinder one after the other down with a wooden wedge. If the pusher is fed more than 0.1 mm, it must be replaced (since pushers cannot be repaired).
Repeat this procedure for other cylinders. To do this, set the corresponding cylinder to the TDC position. TDC is set if the camshaft lobes evenly show up on the controlled cylinder.
Replacing the hydraulic pusher
Remove camshaft.
Pull out the old poppet.
Lightly oil the new pushrod guide and insert the pushrod.
Reinstall the camshaft.
After installing a new poppet, do not start the engine for 30 minutes! He must first «sit down». Otherwise, the valves may collide with the pistons.
Turn the engine over by hand first.
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