Case Study - E38 - Noisy Tappets
|Date of manufacture
When I first bought the car there was no tappet noise at all, only a slight general top-end rustling which is a 'feature' of the Vanos system. After a few months there was a distinct tappet rattle from the left bank, quite noisy and could just be heard with the bonnet closed. This noise should not be confused with the charcoal-canister ventilation valve which sounds very similar to a noisy tappet.
The M62 has hydraulic valve lifters (as does the M60, M52 and M73) which automatically take up any slack between the cam and the valve stem. It is the engine oil below the cam-follower that creates the hydraulic link and provides the automatic take-up of any clearance. The problems occur when the oil within the cavity is contaminated with air. When this occurs the cam follower compresses the air within the oil first and then gives the valve stem a good clout which is where the noise comes from. The noise is very similar to when a conventional tappet is incorrectly adjusted.
There are no repairs required, the air contamination is caused by driving style, in particular short runs where the engine fails to reach temperature before it is stopped again. The air can be removed from the system quite easily and is a known problem within BMW. The fault and solution can be read here.