Engine Noise ??? OM602 W124 300d 2.5L
 

please listen to this engine. Before and after. I fixed
The problem. The noise was a broken mount for the belt tensioner

https://youtu.be/teTYwyLGsDw before repair

https://youtu.be/u0qhTPaHo6A After tensioner repair

Older description of problem below.

I bought this car a few months ago. The engine noise has been present since i have owned it. All services are up to date. !90,000 miles on engine. Does not smoke and has excellent power. There is NO abnormal noise when over 1800 RPMS.
I rebuilt the injectors with Monark nozzles from Mercedes Source last week. The engine was smoother (not vibrating) but sounded no different. The shop that rebuilt the injectors said one injector was releasing too soon and one was too long. Three were good. I had them all rebuilt with the new monarch injectors.

Let me know your thoughts. I would be appreciative .

Hydraulic valve lifters? Sorry, I'm terrible at diagnosing engine noise in person, worse over the internet.

Bad lifters will knock but clear up as RPM rises. They can be taken apart and cleaned, or replaced with new. I think someone find a source for new that was a very reasonable price, like ten dollars each.

I'm not saying that this is your noise but...
 

When I bought my '93 2.5 Turbo 300D it had a similar sound. It ended up being a missing camshaft lock washer that was left out during a previous repair by a mechanic. The camshaft was traveling from front to back making the noise. It had worn down the teeth on the cam sprocket until they were almost razor sharp.
http://youtu.be/qBeu-Fihu5g

It's hard to tell for sure, but it sounds like a collapsed lifter. Take out the camshaft, and inspect the lifters I bet that one of them is soft.

Could you detect the movement looking through the oil fill hole on the valve cover?

Uh...yes
 

Yeah, you can see it in the video I posted.

Here's the thread Max
 

Can't view the video, but a common rattle on these is a bad belt tensioner shock.

Problem fixed.

https://youtu.be/u0qhTPaHo6A