Trying to adjust valves on an 85 300D, and the first one i tried,# 1 exhaust, went from a little tight to totally tight. Tried turning the cap nut clockwise and counter clockwise, made no difference not even a .002 blade will fit the gap.

Finally called the local Mercedes dealership to ask them whether clockwise or ccw to loosen, and they said counter clockwise. So i turned it a bunch, still totally tight.

Finally the cap nut came totally off, and the gap is still zero.

Not sure if i will even be able to get that cap nut back one, let alone get the proper gap. May have to send the car to the crusher.