...just do it. I had the parts to do chain, upper rails and tensioner in my garage from 92,000 to 112,000 miles. Was too intimidated to attempt it. Until August 2nd. Appears that the tensioner didn't tension itself any longer, resulting in sloppy chain which broke the upper rails on the left. That event took out the lower left rail (found pieces of it in the oil pan and matched part number) and bent all 4 exhaust valves on the left side when she jumped timing. Because i didn't do what seemed hard, i ended up removing timing cover, do the heads, and the engine was salvaged by doing too much work and spending too much money when it was all avoidable!! Lessons learned:
1. There is too much first hand knowledge, both professional and experienced ametuer, on this forum to ignore. I listen closer now.
2. Old chain--virtually the same length as the new one. Thomaspin had alluded in some posts that chain stretch may not be the root cause of the problem--might have some merit.
3. Top rails get very brittle. Period. They can snap if something hits them (like the chain). Lower left rail broke from hard impact, but was not as crystalized as the uppers.
4. Chain tensioner--All right, this is my first time and i'm an insurance agent with no mechanical training, but in my opinion the tensioner seems vital to this equation. With no hydraulic pressure applied, the old tensioner was a whimp compared to the new. Is this what allows the chain to slap, breaking upper rails, jumping left cam timing, bending valves, breaking lower rails, runining engines or causing huge amounts of work when tensioner and rails at 100,000 and same plus chain at 200,000 would be much simpler???
5. I have now virtually torn down the top end of an engine and put it back together and it runs. Fairly well. That is a tribute to this forum and its members, and to MB's engineering. I would have destroyed any other engine by waiting too long, instead i got a great education.
6. Now that i've gone this far, i will not be intimidated by a difficult task again, in vehicles or in life. I know that avoiding the difficult will result in facing the near impossible.
Thanks for listening. In summary, change the rails and tensioner before i'm forced to come do it myself under cover of darkness