I have had my 90 420sel reworked with a timing chain job about 6-8 months ago. Everything has been fine. All of a sudden, my car started running extremely rough. When checked by a German Motors shop with and found plugs and wires were bad. That has been replaced and now I have noticed a tapping noise. They checked the timing chain and the cams. He stated there was a very, very minimal space more than should be with the cam. (I don't understand fully) He did say that with the minimal space there was nothing that could be done to reduce it. I didn't think anymore about it and of course, didn't ask if there was anything to minimize the noise. But I thought I would ask here before calling back and asking. From all indications, he did not feel it was hurting anything and didn't feel there was anything mechanically that could be done to stop the noise. It is not loud, but it sounds enough that it bugs me. I may have to just live with it. Thanks for any and all help here.