I have seen a few videos of this engine knock on M157 and 278 vehicles but radio silence in terms of what the remedy was. Have a listen.
Noise is almost silent cold...gets worse as it warms up.

Can confirm, cam phasers are locked, all lifters have hydraulic pressure, all the roller rocker arms are good as well.

Frustrated as I have huge time invested in this motor for no real answer.

I could be wrong but I thought I read coils and injectors are the first things to check and change and usually the culprit

Why don't you drain your oil and use liquid moly first and see what happens

Cylinder 4 is where the noise is coming from. Believe connecting rod bearing or wrist pin has failed. Cylinder wall is scored. Top edge of piston oddly shiny, almost appears as if it was hitting cylinder head. Unsure if I am going to install a used 278 or sleeve and rebuild this one.

so from your first post it sounds like you took your engine apart?
were u having performance symptoms?
miles on car?

58,000miles, bore scope showed scoring - engine not yet apart - pulled injectors this evening - curious to have them tested. If one is leaking under pressure it would cause the noise and possibly the clean spot on the cylinder.

Sorry to hear that. if you need any help, advice, recommendation, pricing info on M157/M278 almost new engines or have it rebuild by us let me know.

M157 engines with an absolutely maximum of 200 to 500 km go for like 18.000USD. Engine Upgrade with Darton MID Sleeves, depends on the quality of Connecting Rods and Pistons.Price range 24.000USD to 29.000USD.

You can have a look online on some of our work "YouTube Tasos Moschatos AMG"

Where r u located

Hello there, we are located in UAE.

Hello, I am in similar situations noise, kinds ofnhitting noise at cylinder 2, no misfire or issue with performace at the moment. So what was the solution?

Thanks

You need to bore scope it to be sure but likely bore scoring. We have done several of these since my initial posting. 550 278 engines as of 2015 have steel cylinder liners from the factory. Prior to that, bore scoring is a concern.

Resolution is to either replace the engine with another unknown history or rebuild the one you have. You will require repair sleeves from a manufacturer such as LA Sleeves and a new set of pistons.

Omg, that noise made my butt pucker. Very hard to tell via a video but sounds like it "could" be an exhaust leak? I'm guessing not, but I too would love to hear an update

edit; you posted as I was typing. So that was the deal on that eng? trashed bore? No rod/bearing issues etc? Apparently I just missed the steel and have alum bores. Wth were they thinking?

They were thinking....nah those wont get bore score.... ignoring the old Vega catastrophe to allow MB to pass the CAFE standards ..the oil solenoid directs less oil during the exact time you want more.... Bean counters win again..except for the costs of rebuilding all those ones w alum bores or replacing them.

total ijits.....

I'd love to be part of the team that makes such decisions. I'm in some similar meetings at my work, and the pattern I see (imo) is engineers need a project to keep busy and keep their jobs, so they invent weird crap to work on. Then it fails, duh, costs the company a 100k to 1M, and on to the next BS project. Sometimes they listen to me, but usually I'm ignored because I'm newer and not part of the design team. Sometimes when they ignore me, I later see my suggestion in the next design. F'ers...
Another thing I learned looong ago, is an engineering degree doesn't mean anything unless you have a mechanical brain to back it up. Some of these people are no different than some rando off the street, they just can't comprehend basic mechanical principles. But they have the degree, and if they don't get fired, there they are making my life worse. Like alum cyls in my car, which will no doubt turn my whole car into scrap one day.
Was there really nobody like me in the meetings that said "Alum cyls will bite us in the butt down the road, wtf is wrong with you people? No!" Maybe there were, but ignored. Then years later they can say; "How are those Alum cyls working out?" :o

I had a Vega! A '75 GT, it was sweet. Metallic silver, all black interior, 4-speed w/ posi, modern round speed & tach, bucket seats, fast back, factory wider mag type wheels and wide tires. Holley carb. Basically looked like a mini-Z28.
Alas, at 16 I had $0 to put a V8 in it, which would've been awesome! Then it did the classic head fail and sucked down water like crazy, which also mixed with the oil. So, with no real options, I just drove it without water. It lasted a surprisingly long time! Months. Until one day.... :o