Ulfi, though it's been a long time since I viewed this thread, I see that several things were found since my last post on this topic.
1. banged up rocker (presumably $5 exhaust?)
2. loose timing chain due to a prior head surfacing operation.
Yet, initially, in your first post you said "...valve clearance and return spring has been checked and found not guilty." and "A recent compression test didn't come up with any clues either."
What bothers me, and should bother you, is that the banged up rocker found should have been evident when valve clearance was checked. The loose timing chain, which created a 10 degree offset in timing should have been evident as a likely culprit during valve gap checks... being off by 10 degrees... or having a 10 degree "free-play" in one direction should have been more/less obvious to an experienced mechanic.
Basically, in the final analysis it sounds like your valve timing relative to cylinder position was off by 10 degrees, along with a "banged up rocker." Have you considered a different mechanic for future work on your car?
Interesting how a symptom of one problem (pinging on one cylinder, but no others) is evidense of related other symptoms (jerky driving) and their common root problem.
