Timm's BMW E31, E32 and E38 Noisy Tappet Cure
There has been many comments about noisy tappets on the
V8 engines, only recently have I come across the official reason for this
problem and how to fix it where possible.
The M60, M62 and M52 engines use Hydraulic lifters which take up all the back-lash between the cam and the lifter. To do this the lifter cavities must be completely full of oil, if there is any gap then the cam clouts the lifter instead of smoothly following each other. There are a number of reasons that the Hydraulic Valve Actuator (HVA) gets air trapped:
The oil is too viscous (especially when cold)
Frequent short journeys
Sharp cornering with low oil level
Frequent short journeys where the engine oil does not reach temperature means that the oil can absorb air when it contracts in the supply gallery. The air is normally expelled when the oil reaches high temperatures but where the oil never reaches high temperatures the air can be a problem, especially where it has to replenish the oil in the HVA elements. Small amounts of air are not really noticeable but where it builds up over a few short journeys the HVA elements will begin to be noisy.
The sharp cornering problem when the oil level is low is more obvious, the oil-pickup slurps air instead of oil and this is passed to the HVA elements where it can be trapped.
Where the oil is too viscous it cannot replenish the HVA cavities especially when the engine is cold. The oil in the HVA cavity contracts as the engine cools after a journey and in this way air finds its way into the system, if the oil is too viscous it will not immediately replenish the cavity.
How to fix the problem
Firstly, get the correct viscosity oil, you will not cure the problem if the oil is too viscous.
The procedure is pretty simple and is designed to bleed the HVA elements:
Check the oil level, replenish if necessary. Run the engine at idle and listen for noisy tappets, if the tappets are noisy run the engine at 3000RPM (with the car stationary) for 3 minutes. Return the car to idle for 30 seconds (to achieve minimum oil pressure) and listen for noisy tappets. If a tappet is still noisy increase engine speed to 3000RPM again for 3 minutes.
It is possible that you may have to repeat this procedure 5 times to bleed the tappets correctly. If the problem persists there may be another problem but in most cases this will provide the cure.