Well, today I did the "unscrew the lines one at a time" test. None of the individual injectors removed the knocking when disabled.

I then popped the valve cover off to check the valve clearance again.

I think I am going to put it back together and move on to other things. I still have the motor mounts to do, and I haven't done an oil change since I got the car... maybe new oil will quiet it down I can always hope

It sounds more like a hard tap than a fuel knock. I would check the vacuum pump for a soft or broken spring. A bad spring will allow the follower to rise off the ramp. It will then land with a clack sound. More prevalent at an idle than high speed.

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

How tight should the timing chain be on a 1982 300D (turbo)? Should it be real tight? I can wiggle mine with my fingers, it's got a little bit of slack.

I did install a new key to correct fro _stretch_, and I installed the tensioner spring when I did this.... is that sufficient to rule the chain tension out?

what you did was sufficient.

no one can tell you how tight the chain should be because they are not brave enough to remove the valve cover, start the engine, and put their fingers on the timing chain.

the looseness of the chain @ 0 rpm is mostly meaningless.

your chain tension is most likely fine.

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I put her back together last night; still the same knock, don't know what else to do...

I cannot pinpoint the source, other than (1) it is in the front of the motor and (2) it is not at the crankshaft, which is good I guess.

Beyond that, the sound travels through all the metal parts, so I cannot narrow it down. Yea I am using the HF stethoscope...

This weekend I am going to finish working on the headlights and maybe replace the motor mounts, they are totally shot and cracked, you can see it easily.