My 78 300SD started making a lifter tap noise when under light load only. I suspected an injector was failing at first. The noise has progressed and now makes noise all the time. I tried to locate the cylinder making noise by cracking injectors (a long shot on valve noise...but it was quick and easy). No luck. It is definitely a mechanical noise because it does it when engine braking and shutting off the key, eliminating the chance it is a combustion noise. I checked my valve clearance, and the re-adjusted them all. The camshaft lobes look OK to me, no broken valve springs, it all looks OK. I'm convinced the noise is in the upper end. It is loud enough to attact the attention of people I pass on the street, and pretty obnoxious in the car. I really don't want to start tearing it apart to diagnose this noise. Has anyone experienced something similar that might be able to offer some advice here? Any help appreciated.
Joe

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1978 300SD
Running Biodiesel/SVO, 2 tank system
127,000 Miles

I took the valve cover off and ran the engine. There is no change if I put pressure on the followers with a screwdriver as it's running, so it doesn't act like a valve clearance problem. There is a tensioner/slider on the back side of the chain (I'm sure many of you know that), If I put pressure on that slider, moving it tighter to the chain i feel a bump in it that corresponds to the tapping noise. Also as soon as I shut it off, there is slop in that slider. Should that thing hold tensioning pressure after the engine is off? It doesn't appear sloppy with ther engine indling. Lastly, now that I've fooled around in there, the noise is gone except when I throttle the engine, which you can only do with the valve cover back on.
Joe

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1978 300SD
Running Biodiesel/SVO, 2 tank system
127,000 Miles

Can you tell us what the chain touches before and after the item you are describing ? By ' backside' of the chain... what do you mean ?

I mean it rides on the outer side of the chain, as opposed to the cam/crank gear side. It is the last thing to touch the chain before it gets to the cam gear.
Joe

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1978 300SD
Running Biodiesel/SVO, 2 tank system
127,000 Miles

And your engine is a non turbo ?
Ok,, you know which way the chain travels... (?)... so this is on the passenger side of the engine ?

No, it's a 5cyl turbo.
The chain travels clockwise when looking at it from the front, and the tensioner is on the passenger side of the engine.
What made you think it was a non-turbo?
Joe

__________________
1978 300SD
Running Biodiesel/SVO, 2 tank system
127,000 Miles