The Mercedes coupe has been a lugger for top starting performance .In interest of getting a much better runner / starter out of the old 617 motor is their any tips or write-ups you can recommend.The old bolts concern me the most,when it comes to exhaust parts it seems inevitable their will be trouble with stripping or flat out breaking a part .The forum members here at P.P. are experienced and Ive read a few threads about this issue ,the feed back is greatly appriciated . I guess dos and donts are what Im asking here from those who"ve tackled this undertaking.The parts have been ordered and should be here friday so I can take my time cleaning and setting up the job first before reassemble . A few videos describe burning the material out ,others use oven cleaner to approach the crub ,my suspicion is their is a lot of carbon build up in their once Ive open up the assembly ,it may need a radiator shop who will allow this crud in their tank cleaner.This is an old 617 and mileage has been creeping into the 500k area so its needing abit more than the glow plugs addressed this time ,hoping for the best. Again ,thanks for your input.

The Manifold studs on the 617.952 only have like 4 threads that screw into the cylinder head.

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84 300D, 82 Volvo 244Gl Diesel

Boil that sucker, if you can.

-Rog

I've cleaned the manifolds on most of my cars. Took them (both aluminum and cast iron) to a engine machine shop and they did it for $60 or less.

I had one of them media blast a 603 intake for me and boil it. $50. Totally worth it.


I would suggest painting them once you've had them cleaned.

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Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

+1 if there's a machine shop handy. Otherwise, if you decide to clean them yourself, wear two pair of nitrile gloves under a pair of chemical resistant gloves. Otherwise your hands will be like coal for a week.

Biodiesel 100% works great for dissolving the intake goo.

It will make a huge mess, but it will also make a huge improvement particularly on an engine with an EGR valve.

Bio is pretty benign to your skin, so you just have to protect yourself from getting the dissolved goo on you which will stain your skin, or whatever else it touches.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The egr piece unbolted fine its the stainless sleeved tube at the mount on the exhaust thats not budging ,the sleeved clamp is totally off the joint ,wont budge.How much carbon is evident with this not wanting to release .Anyone ever run into this issue?

My SDL had a HEAVILY sooted up intake manifold. EGR valve had sealed itself off from all the soot and my corrugated tube was also stuck firmly in place. I gave it a whack with a rubber mallet and it came loose.

In my case, I'd have to take the manifold a couple hours to the nearest machine shop, so I decided to try de-gunking the manifold myself. I just dumped it in a vat of 50/50 degreaser and water and left it for a week. Came back with a wire tube brush and it cleaned right out like softened butter. NASTY JOB!

In my case, the intake runners were so choked down that the poor engine was breathing through a hole about 1/2" in diameter You could not believe the amount of soot and tar that came out of that manifold, but when I was done with it, squeaky clean! I'm sure it isn't now, but at least the EGR is blocked off to prevent future sooting!

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

It does take a wack or two ,thanks.The exhaust manifold does need to come off ,right, or will the intake be the only bolts to decrude.I still need the intake mount off so its not a clear view as of yet.

If you are not in a rush, why not wait and replace both the intake and exhaust manifolds with those from a 1978-79 W116 300SD?.
Junkyard pricing will be reasonable and it will cleanup the engine bay a bit.
There is better exhaust flow without the EGR port on the exhaust manifold.
Typically, there is no need to clean the inside of non-EGR turbo intake manifold as they don't get gunked up in the first place.

Unobtainium W115 long runner intakes also can still be found in the junkyards on occasion (I've pulled 6 and sold 2).
Changing to a W115 long runner intake will require clocking the turbo, changing the turbo to air intake connector, changing the air filter setup, and changing the crankcase vapor recovery system.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Removing the intake manifold from what I assume is your 1983 W123 300 CD is fairly straightforward.
(You may want to add your vehicle to your signature, or reference it in your posts or thread title)

FSM job # 14-450

A couple of tips:
Pre-soak the exhaust stud nuts with your penetrant of choice (PB Blaster, etc.).
Run the engine for a few minutes to safely apply heat to the exhaust nuts.
Apply some more penetrant after turning off the engine.
Use a six point socket on the nuts.
Use a short pipe on the handle of your socket wrench (or use a breaker bar) to break the nuts loose.
On a really stuck fastener, sometimes tightening the fastener a little will break the corrosion seal allowing you to then loosen the fastener.

For future reference here is a link to the W123 FSM

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

A few tips about approaching this task again is to completely take the aircleaner assembly off /soak the oiley areas with engine cleaner(alot),pressure wash til its clean ,damn their is some oil laden metal parts under here,of coarse wrap that alternator before sending the water and oil flying everyhere .Ok , its not crazy hard,but its a good amount of bolts with various challenges getting too a few of them.You do have some hidden items like one mounted at the bottom ,a 17mm that is more of a support to the whole turbo / exhaust assembly.The oil supply drain requires you torq your arms in the engine bay just so for reaching under and in to their location .A couple of heat sheilds ,remove some lines and cables.A Big box IS RECOMMENDED with 4 other smaller coffee cans to gather parts.Then go clean that intake.This one was not terrible ,but it will be nice to run a clean one and get new gaskets and seals were needed. This project screams the need for new seals at the turbo drain ,the return air recovery under the air cleaner .If youve replaced a starter on a 617 youll also see the advantages of getting it done at this time of disassemble .New,New,new,new,new! Cant wait for first start up .