Thank you for the replies. FYI I am working with a retired Mercedes dealer mechanic He has checked the timing chain early on (single). We were able to run the engine with the valve covers off with no evidence of a valve problem. Also if you spun the engine with out spark the knock was not present. I am aware not to turn engine backwards but this was done as a last resort after the engine locked up knowing I was going to have to pull the engine and either tear it down or junk it. I will borrow a bore scope this week end. Also is there a good thread on removal?