Question here on the timing chain tightener on a 1981 300SD.
I had stuck this used engine in the 300SD last spring. Have had some considerable problems with the used. (Does the expression NEVER AGAIN, mean anything here?) Worked through most of the trouble. I took the car to an MB Guru here and he listened for a moment and told me that upper end noise was most likely coming from the timing chain. He recommended I remove the tensioner and make sure it was working properly. He showed me a new one and it has spring that pushes a rod out. When working properly the rod will not back up, it ratchets out. He explained that the rod should be shoved out and then pushed back into the back side. He guessed the rod was out too far and the chain was too tight.
I pulled the tensioner and found it just slid back and forth. I then cleaned it overnight in some parts cleaner. Next day it began to work a little better. Reassembled and did a valve adjustment while I was at it.
Sounds better, especially at idle. But I still detect a ticking noise at middle range RPM's. Seems to be quieter, but is definetly still there.
I did note that with the cleanup the tensioner still will back up, just not as freely. I also noticed the tensioner fully extends.
My questions are, should I replace the tensioner? Next question is it now time to replace the timing chain also? Anybody have any experience here with this?

Sounds like you need a new tensioner. I your chain jumps, it will cost many times the cost of a new tensioner.

I was lucky, Mine was stuck and not putting any tension on the chain and I caught it (while adjusting the valves) before a cross country trip. Could you see the chain jumping in the middle of the desert?

Fastlane has new tensioners at reasonable prices. I paid over $100 before I learned of thes site and Fastlane.

P E H