I just went to adjust the valves on my 1984 300SD (412,000+ miles) and got to valve 4. I did all the others and it went well. This is not my first time. I bought this car in 1998.

Anyway, here is my problem. The number 4 won't adjust. I think the cap nut has bottomed out. Have I lost my mind? Am I forgetting something after doing this a bunch of times in the last 14 years?

I loosened the cap and log bolts. Turned the lock bolt clockwise to gain some clearance. Turned the cap bolt clockwise to adjust the valve clearance and...nothing. Repeated several times until the cap bolt turns the valve and there is still distance between the lock and cap.