The top nut that contacts the rocker arm is the locknut and the bottom one is the adjuster. When you turn the adjuster, if the big collar that holds the valve spring turns, you'll have to find a way to hold it in place or turning the nut won't make any adjustment. They probably won't all move, I think about half of my big collar nuts moved. I used channel locks to hold the big nut in place while I turned the adjusting nut. Make sure you tighten down the locknut when re-checking the clearance.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo