I recently bought a 1985 190e. I was told that it had just had a valve job, and it looked like the head had been hot tanked. Within a few hundred miles there was some serious valve noise so I pulled the v cover, and this is what I found: all eight of the tappet contact seats are missing AND the cam gear is almost gone, literally ground away from the back forward by the chain. Since this is the first MB I've worked on, I went out and got a manual. From the photos in it, the cam gear seems to be located on the cam correctly. All the rocker arms are nicely aligned with the cam lobes. The chain and all but the cam gear are aligned straight. The cam gear is about a quarter of an inch too far back to be aligned with everything else that the chain goes through, over, on, etc.

The tappet noise is a no brainer, it’s coming from the absence of the tappet contact seats. (The top of each valve stem now has a worn, cup shaped area at the valve stem end, thank you norm's auto repair, San Jose, CA).
However, the cam gear is another can-o-worms. I can't see any way to realign the cam gear with the rest of the gears, guides, and chain. What would cause this? How to fix the situation?

How tight is the chain. That motor has a ratcheting chain tentioner and I hear of instances every year where someone has a head off and doesn't do the proper disassembly and install of the tentioner. This makes the chain over tight and often breaks the cam.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

look closely at a new gear. I think there is a definite offset of the teeth in respect to the hub. Puttin one on 'backwards' will definitely cause serious misalignment and rapid self destruction. There is also usually (no sure on your engine) a thick (3MM+/-) thrust washer between the sprocket and fron cam tower. Be sure and replace the chain and the gear and any worn guides., and give yourself a big congratulations for searching for the problem before it trashed the engine.