Mercedes-Benz W201 hydraulic valve lifter tapping
Mercedes-Benz W201 M102: is valve train tapping when cold normal?
Hydraulic valve lifters can tap after starting, when oil has not yet filled them. The noise usually stops as the engine warms up or after a few hundred metres of driving, and it usually does not affect power. If the rattle continues for over a minute, a lifter is probably faulty or leaking.
What should you do if the Mercedes-Benz W201 lifters tap constantly?
Hydraulic lifters have no adjustment. A dirty lifter can be cleaned and filled with fresh oil, or the whole set can be replaced with new ones. Before dismantling, cover the openings in the head so that small parts do not fall into the engine. Even a new set of lifters does not always remove the noise completely.
What else besides the lifters can cause tapping?
A worn camshaft can cause a similar noise, and it also reduces power. The condition of the cam lobes can be seen by removing the valve cover, so check it before ordering lifters. Blocked oil holes in the head can also make the lifters tap.