W114 250 CE valve adjustment "ventile spiel messen"

Hello everyone,

I'd like to share with you my first experience adjusting the valves on my W114 250 CE. I'll conclude with a few remaining questions.

After installing new spark plugs and driving a quarter tank of gas, I took a picture of the spark plugs (see photo). As you can see, cylinder 4 really stands out. I decided to check the valve clearance and readjust it. Hopefully, I'll know soon whether the spark plug in cylinder 4 is no longer fouling and whether the root cause was excessive intake valve clearance.

Make sure you have the correct socket wrench: the Hazet 2768-1 with a width of 17.05 mm, not the Chinese replicas with a width of 17.3 mm that easily slip off (see photo of socket wrenches). I was fortunate enough to quickly obtain an original Hazet through Kleinanzeigen. To minimize the amount of manual crankshaft rotation clockwise (660 degrees) required for adjusting the cylinder sequence 1-5-3-6-2-4, I found it helpful to make a paper ring around the distributor, marking it every 60 degrees to find the correct camshaft position (see top view of the distributor). You also need to remove the rocker arm springs from the intake valves to properly position the cap around the nut and create the correct rotational stroke. This isn't necessary for the exhaust valves; see the photo with the required valve clearance and a photo of the spring I had to remove.

Questions:
1) See the photo of the valve clearance measurements and look at cylinder 4. Could this explain the different colors of spark plug 4? (Once I've used a quarter tank of gas, I'll take more photos and upload them. For now, I've cleaned spark plug 4 and swapped it with cylinder 3.)
2) See the photo of the cross-section of the rocker arm. How does the combination of "kugelbolzen" and "gewindebolzen" prevent the adjustment from slipping/moving? I understand that the adjustment torque must be at least 20-35 Nm. In my case, it was much higher. I see that the "kugelbolzen" have external threads at two places, and I think the "gewindebolzen" have the same internal thread along their entire length. However, how does the construction ensure this doesn't move any more? Differential threads or slightly oval thread shapes?

I look forward to your feedback.

Regards, Marc