I would like to discuss in exquisite detail the MB design process on their exhausts for a 617 300D.

The reason for this is im trying to duplicate as much as the same design process in my van engine conversion.

Ive already done this wrong causing exhaust damage, and I want to make sure I do it properly the second time for long term use and trouble free. I have a few questions on why MB did something a certain way, and so on.

(please excuse the crudity of these drawings)

So in a MB stock exhaust for a turbo 300D drawn here, the flex pipe (1) is before a soft mount on the bell housing (2), and then continues with no additional supports until the 4 mounts on the rear muffler (3-6).



What I did on my van was this-

The downpipe was hard mounted to the bell housing (1), continued to a flex pipe (2), and soft mounted in positions 3, 4, and 5, with rubber hangars.



After 8k miles, positions 1, 3, and 5 in the above diagram were broken completely off.

What ive done now in addition to MB stock motor mounts is purchase a MB stock downpipe, so I have the stock location, and stock arrangement for a downpipe, then I intend to do a soft mount on the bell housing like MB, and I guess my two questions are this-

Why is the MB flexpipe before a rubber mount on the transmission bell housing? Wouldn't that take most of the function of the flexible downpipe out of the equation? Or does that arrangement actually dampen excessive flex pipe movement? I know it works, im just trying to understand why, so when I go to try and do it as close as possible I know the reason why something was designed such a way and make sure I keep that in mind, not just that its the way the factory did it.

And do the 4 mounts at the extreme other end of the exhaust mean that exhaust vibration and movement are compensated for in the distance of the unsupported exhaust somewhat?

Should I try and do the same thing with no mounts on the front side of my muffler?

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This post brought to you by Carl's Jr.

The stock system is mounted in rubber at every point except where it attaches to the engine. There is vibration and with the 617 there is that "hop" at idle which produces a lot of movement. I recommend trying to duplicate as much as possible the way it was done at the factory. The vibration of metal to metal is what causes fatigue and breaking.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

yup, the one hard mount was one of my big mistakes, even though it came before a flexible joint.

This is what brings me to my next question, is the flex pipe on a MB dealing more with compression vibration, or bending vibration?

The mounting in a vertical position right before a fairly restrictive rubber mount leads me to believe that the flex pipe is dealing with a specific angle of vibration more than anything, like an accordian moving in and out more than bending back and forth. What do you think?

Im thinking the flex pipe I included didn't handle the most common type of vibration I was going to see, since it was horizontal

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This post brought to you by Carl's Jr.

Neither. The head pipe will expand and contract a great deal with temperature and remember it will do so primarily along it's length (not much change in diameter). You gave it no place to "grow" so it broke itself apart - hence the flex section up by the turbo in the stock system. Mimic the stock system and you should be fine.

Dan

I thought the bellows took care of most of the expansion and contraction issues of heat though, right after the turbo instead of the actual downpipe?

Still, you have a point as I was also missing the bellows anyway.

I can definitely see the lack of a bellows doing the job of cracking off a welded steel mount

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This post brought to you by Carl's Jr.

I think what you're calling a bellows is there to absorb the majority of the expansion. I picked up from your Picasso-like artwork (I like it!) that it was deleted and replaced by an expansion joint AFTER the solid bellhousing mount. I think that was the source of the issues.

Dan

yeah, I had quite a space issue, and could not get a good downpipe in there without removing whatever that thing is called, expansion joint/bellows ect.

It seemed like a clever solution at the time, but could certainly be the cause of all the damage. Worth remembering from now on for me. The idea originally with the hard mount was to provide the second support bracket that was missing from removing the bellows thing from the turbo, but that took no account for expansion at all.

Picasso like drawings are the result of being left handing and drawing in paint with my right hand on a computer, glad you like them!

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This post brought to you by Carl's Jr.

Huh? Can't you use your left hand on your computer? Or would that ruin your Picasso drawings?

My mouse is on the left side and the buttons are flipped, so the left hand index finger presses the right mouse button and that's the major clip button. "right mouse button clicks" are now left button for me.

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daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
Cluster Needles Paint
New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more

On my conversion (617a-> 107) I used the stock configuration all the way to the first joint. I then added a 14" "adapter" which essentially was where the Cat was on the 380SL and mated it to the stock SL exhaust to the rear. I did have to replace the MB flex joint with a stainless wire mesh one because it was broken in half. It's been fine through pushing 40k miles, so if you can replicate the design of that first section I think you'll be just fine.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

I just ran new exaust on my 300TD and used simple rubber mounted hangers.
I tack welded the hangers on the car and a round metal rod to the pipe. The round metal rod slides in the rubber mount.
It's just exaust and not rocket science, just as long as the pipe is not mounted solid and is on some type rubber hanger where as you have some give all will be well.
The only way I could see me having problems is if the motor mount s broke and the engine
Had a lot more wiggle than usual, and even I think mine would still be fine.
I will take photos of my hangers if I get a chance tonight.

its not rocket science until you start altering stock usually non replaced items in custom applications. Then you can overlook something that causes problems, something that usually would be a non issue when redoing a factory exhaust system.
Already ive retained some useful info from this thread, which is the amount of heat expansion that I should have compensated for, and did not when I removed the bellows to mount my downpipe. Even more importantly to me, its a lesson that im going to apply to another project nearing the exhaust manufacturing phase, where I had almost jigged up the same failure. This means a different manifold design for me to keep the factory bellows

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This post brought to you by Carl's Jr.

if I were doing more CAD related stuff, id probably do what you do, but my mouse use habit is highly ingrained at this point

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This post brought to you by Carl's Jr.

You won't believe how I'm going to run the exhaust on the S-10 - THRU the RF fender! Remember, this is a race truck. So I'll run the flex joint off the turbo and the factory head pipe turned about 90* then thru a hole I'll drill in the sheetmetal. It may need a little more bend in it - I'll have to mock it up to see where it falls. Pics when I get that in place.

The tricky part about my set-up is that I'll have to be careful to cool off the engine before I shut off the engine so I don't fry the valves. I have to idle back to the pits after the run anyhow so I expect that the exhaust temp will drop to safe levels as I drive.

Dan