I've spent the past month chipping away at this repair, soaking the manifold studs/nuts with Kroil (fancy version of PB Blaster, penetrating oil), running the engine to heat cycle (makes the oil wick in more effectively), and twisting, contorting, and cutting up my arms to get the ratchet in there.

Managed to get the forward most top 3 out perfectly cleanly, the rear 3 marked in the diagram are loose (L), and the front two in the bottom row I can get the socket on, they're just too tight so I'm going to continue with the penetrant and heat cycling.

That center stud/nut on the bottom row, I don't see any way of getting to short of removing that motor mount or making a custom tool.

Anyone with experience have advice?

I want to do the motor mounts while I'm in there (front prop shaft and right exhaust line/cat already removed), but I heard it's an absolute nightmare job even with as much access as I have?

After talking to an AI, it seems I can lift the engine from the bay with a support bar just a bit, 15-25mm and that will allow the mount to fall out?

I want a high quality replacement; Corteco? OE Mercedes? Those are the two FCP Euro stocks. I hear LEMFÖRDER recommended but don't see them stocked online.

Also regarding the prop shaft, AutohauzAZ stocks Febi Bilstein and Powertrain in the same price bracket. I'm hoping I'll be okay with one of those because the Dorman OE Fix prop shaft is $800

You Tube

 

Such a nightmare job. I had a leak in my W204 passenger side exhaust manifold gasket M272 engine. I connected a long spray can straw to my boroscope to be able to spray down every nut for over a week. I bought an articulating ratchet at harbor freight to get the socket on the nuts. I still ended up snapping studs. Finally brought it to my local MB dealer where they removed the head to replace the manifold. That stupid engine mount is in the way.

I will say from your photos your looks in much better condition than mine. I bought a used manifold from an Arizona salvage yard that looked almost new after i cleaned it up. Good thing I did because the old manifold was all pitted along the gasket side.

 

That is absolutely wild!!!

You did and went through the same process!!!

Bonkers that we both ended up using the same technique.
Now I wonder if the AI I used found your post and suggested it to me but with some tweaks.

Which stud was it that broke?

 

I broke cyl 1 upper stud. It was right next to the exhaust leak. I got the lower one to start spinning so attempted the next one, I felt it turn a little so I went to tighten it and SNAP. I probably should not have done that, maybe it would have not broken, who knows. The stud broke outboard of the head so maybe I could have fit vise grips on to spin it out but I tried with the manifold still on and couldnt grip it.

I was just so stressed out over it I had to bring it to MB to fix so I know it was at least done right. If I had a garage to work in maybe I would have tried more.

 

mgiara, that sucks
I can say I would never refer to Kroil as fancy, nor would I use it for anything, period. There's a guy at my work that insists it's the best thing since sliced bread. He's 70 and used it in the Navy, and I think the smell brings back memories of the glory days? I've even shown him that basic WD-40 works better for his favorite usage, and doesn't stink up the whole building, but he still uses the Kroil. Then I found a youtube video from Project Farm where he tested various penetrating oils on rusty bolts. Kroil came in last place and basically equal with the bolts where nothing was used. If I recall, the most effective was heat, which most rednecks like myself already knew.

So I would soak in Liq-Wrench or similar, or tranny fluid. Ideally when hot, but not so hot it smokes the oil. Also ideally let it soak for a s long as you can. A day if possible, or more, and the heat/soaking several times a day? How much effort you put in is based on how much of a nightmare it would be if the bolt broke. When I plan on doing a job and I think some fasteners may give me grief, I'll start soaking them days or weeks in advance. Just a quick squirt here and there when you think about it could save you a massive headache later.
If you can get the nut to move at all, in either direction, use that to get more oil in. Say it moves a mere 2 degrees, you keep it soaked in lube while moving back n forth that 2 degrees until you feel it become 3, then 4 etc. Also try heat but stop when it starts burning the oil out. If still nothing, heat until red and try, then re-saturate with oil and continue. Basically you're just desperate at this point and trying various things.

In a case like this you also apply the oil at the gasket area so it can get to the threads on the head side too, because those threads may break free first.
Then knowing from experience about how much torque they can take before breaking, you try loosening it. If it won't move, you heat the bejeezez out of that nut. Cherry red if you have to. If in a hurry you can go straight to heating the nut.
Another option, if you have room, is to cut the nut off. I've used a Die Grinder with a cutting disk, or a Dremel with a Diamond disk, even a chisel. That nut looks like Copper so it would be (would have been) easy to cut off if you had access.

Since you already broke it, I would apply all the above to the stud, once the manifold is off. Of course Vice-Grips will be your new wrench to remove it.
The following applies to nuts bolts and studs with rust, which you can try at any point but usually it's when all fails:
Heat to burn the oil out, let cool and soak in Phosphoric Acid. Not Naval Jelly, but liquid Phosphoric Acid. I bought mine from a paint and body shop that primarily sold to car paint shops. Might be available online? Apply several times a day, or every hour, or whatever you can. This stuff eats the rust, but takes time to get in there and do its job. Same deal with trying to wiggle the fastener to help it get in there as best you can, and get more in there as you go.
Once out you may opt to spend a little time getting medieval on the fastener, which I have done a few times using oxy/acetylene torch and hammer because at that point I wanted blood.

The only time the above has failed me is when the bolt was simply so rusted that it was too weak to crank on. If so, you have to decide if you can do without the bolt, or have to drill it out and possibly Helicoil or Keensert it.

I wish you the best of luck! Let us know what happens and what worked

 

I was switching off between PB Blaster and Liquid Wrench when spraying the nuts/studs. I was driving the car in between spraying them down. I was paranoid about the engine bay going up in flames while driving but it just smoked alot. I also used the toothbrush looking wire brushes to try and scrub off as much rust from the threads as I could.

Also when removing the bolts holding the cat pipe to the manifold the square copper looking nuts on the manifold came off. There are instructions in the manual for reinstalling them but I had the new/used manifold to install

I cut the old manifold up to see what it looks like in there for fun. I found it interesting how its made.

 

I see, thanks for that.

I can relate to the stress part. This has been an unbelievably stressful journey.

Also, myyyyyyyy goodness, the number of times I've said EXACTLY that to myself.
Mine is parked on the street.
Extremely sketchy being under it, especially considering how HEAVY it is, with cars buzzing by a few inches away.

 

TimC300 is the one who snapped a stud. I haven't (yet fingers crossed), but all the short-measures done by the previous owner backfiring on me, yes that absolutely DOES suck.
"Kroil came in last place" <- this is 100% your memory lying to you.
In that video, all penetrants performed about the same.
Kroil is widely and consistently ranked among the top 2-3 penetrants on the market.
"basically equal with the bolts where nothing was used." <- your memory is bold-faced lying to you here.
I fact-checked this; it's completely untrue and I can show you the research I did.

This is exactly what I'm doing, but I wouldn't call it desperate. I would call this "the smart way".

Currently, of the 3 I've successfully removed and the 3 I've successfully loosened, the stud came out completely; the nuts barely unthreaded off the studs.
Another detail: if you heat the manifold + engine block, CRC, manufacturer of Brakleen makes a product called Freeze-Off
When you heat the whole area, all of the metal expands.
The idea behind Freeze-Off is, once the whole area is warm, spraying the product on ONLY the stud will rapidly cool the stud, causing it to contract, while the surrounding area (manifold flange and engine block) remain expanded.
I might give this product a try this weekend if I don't make progress.

Haha! Thanks. Again it was TimC who snapped a stud. I might still get lucky, again fingers crossed
If I snapped a stud and had ANY shank left to grab on to, I would buy a proper high quality stud extractor.
They're simply far more effective at stud extraction than any other tool.

Thank you sir!!! 🫡
Very much appreciated.
I've been posting this entire saga to a W212 Facebook group when I SHOULD have been posting everything here.

98% of that Facebook group are non-mechanically-inclined people who are mostly curious about aftermarket modifications.

I'm here to wrench.

 

Freeze-off, yes. I had forgot I had tried that but it wasnted Freeze-off. I went to the dollar store and bought a few cans of the electronics dusters. If you spray it with the can upside down its freezing cold.




I had tried that on the two bolts holding the cat to the manifold. To heat the bolts I only had a small benzomatic tourch I use for soldering. They were so rusted I couldnt even see threads just a mass of rust.





On mine the exhaust manifold is so close to the engine mount I can not even fit the special wrench they sell to remove the engine mount bolt. I was thinking I may have more room if i can lift the engine up more. Maybe if I took a grinder to the tool it would have. I was able to fit a 16mm stubby wrench on but not much I can do for leverage. Maybe MB has a more special wrench for it. I have since bought a little welder from Amazon, if I had it back them I would have tried making a special wrench.

 

Something else I just remembered looking thru photos is how i was having trouble getting a socket on some of the nuts specifically the bottom one near the engine mount. I bought a 10mm 1/4" drive socket set off Amazon that allowed me to get to them. I practiced reaching the nuts on the new manifold to see if the ratchet would fit.

I bought the set mostly for the intermediate height socket. I remember drilling out the hole inside that goes thru the socket so the stud would fit otherwise it would bottom out on the stud and not fit all the way down on the nut.

And then the harbor freight ratchet i bought seemed like a good idea. I was able to fit the socket on with my left hand while holding the ratchet handle up top out of the way.