Repair or Replace? (Exhaust pipe crack - [Photo]) - Page 3 - PeachParts Mercedes-Benz Forum

280EZRider · #31 08-21-2009, 03:06 PM

Quote:

Originally Posted by EricSilver

Aahhh... Delightful silence.

I have a ring of PC Fahrenheit over the crack. (Installation: Thin layer of PC Fahrenheit; foil strip; then successive rings of PC.) Smoothed and shaped, it looks like a slight extension of the neck of the muffler. If painted gray, you would likely not know it was there. Should last long enough for me to find a welder.

Nice job - for the interim.

Kestas · #32 08-21-2009, 03:15 PM

The picture shows the crack is at a weld area. Stainless steel exhaust systems are prone to cracking from a phenomenon called "sensitization". This results in stress corrosion cracking and is a common failure mode for stainless steel exhaust systems, and universally occurs at welds.

Resistance to this type of cracking is dependant on how the supplier fabricates the exhaust system. Unfortunately, there is no way for the manufacturer to determine the quality of the fabrication and how sensitized the welds are until it is caught by their warranty system and a laboratory investigation is performed. I've done a lot of laboratory investigations on this exact phenomenon.

EricSilver · #33 08-21-2009, 03:55 PM

Quote:

Originally Posted by Kestas

The picture shows the crack is at a weld area. Stainless steel exhaust systems are prone to cracking from a phenomenon called "sensitization". This is a common failure mode for stainless steel exhaust systems, and universally occurs at welds.

And two broken exhaust hangers accelerate the cracking process.

I may end up just replacing the resonator. Seems the simplest of all options.

EricSilver · #34 08-21-2009, 07:06 PM

Another compelling reason for a replacement, or a solid re-weld, is exhaust
back pressure.

I'm definitely noticing the performance gain. Nothing dramatic, but definitely noticeable.

EricSilver · #35 07-07-2010, 12:51 PM

Revisiting this after almost a year.

The epoxy fixed worked -- for a while. I would say a week at most. The epoxy ring stayed on the pipe but the seal did not hold so exhaust gas reseumed leaking, but the noise was not as big an issue.

More recently I removed the epoxy -- easily broke it off by hand (proving how ineffective it was) and did the tin can thing, sort of:

* Cut a 1/2" ring from a bean can.
* Coat inner radius with Permatex Copper gasket maker
* Wrap around cracked part of pipe
* Secure with exhaust clamp.

This will likely be a more permanent solution. I say likely because I am now thinking I should have let the Permatex solidify on the 1/2" ring before attaching it to the pipe. I may yet still do that and am preparing one in the likely event that I do.

#36 07-07-2010, 03:19 PM

Your best bet is to get a piece of sheet metal thicker than a bean can. Clean the area and bend the metal around or whatever necessary to mold it to the shape of the leak. Then MIG it in place. Surely you have a friend with a small 120 Volt MIG welder.

Since the leak was originally due to flexing and not from a rotted pipe, a patch will work fine.

I have a MIG welder and a stick welder. I've done enough sheet metal welding with a stick, that I can use a 5/32" 6011 rod and just stick weld it. If you find someone to weld it with whatever they feel comfortable using, you can fix it once and for all.

Educaid · #37 07-07-2010, 09:43 PM

I've got the same problem so this is timely. I'm not expert but why can't a welding or muffler shop remove the parts, cut off a few inches of the pipe going into the muffler, then weld a new piece of exhaust pipe where the old pipe was cut and weld the other new piece of pipe into the muffler? This was suggeted earlier. I don't see what the big deal is unless there is a problem removing the offending part from the car. I'll let you know what I find out.

#38 07-08-2010, 08:24 AM

Yes, a muffler shop can indeed do this. Anyone who can weld sheet metal can do this.

EricSilver · #39 07-20-2010, 11:35 PM

Thanks, I'll see who I know who has that skill and equipment.

And -- rubbing my eyes -- Larry Bible? I thought you left here several years ago? Welcome back.

Quote:

Originally Posted by LarryBible

Your best bet is to get a piece of sheet metal thicker than a bean can. Clean the area and bend the metal around or whatever necessary to mold it to the shape of the leak. Then MIG it in place. Surely you have a friend with a small 120 Volt MIG welder.

Since the leak was originally due to flexing and not from a rotted pipe, a patch will work fine.

I have a MIG welder and a stick welder. I've done enough sheet metal welding with a stick, that I can use a 5/32" 6011 rod and just stick weld it. If you find someone to weld it with whatever they feel comfortable using, you can fix it once and for all.

mytmousemalibu · #40 07-21-2010, 12:29 AM

Id weld it. Even if rusty, it will just burn back some, no big deal, fill it like a rosette weld if it burns open some. Fixed plenty of stuff like that. Worst case a patch weld over it or section and replace a short piece of pipe.

pifcat2 · #41 07-21-2010, 03:30 PM

Quote:

Originally Posted by EricSilver

Revisiting this after almost a year.

The epoxy fixed worked -- for a while. I would say a week at most. The epoxy ring stayed on the pipe but the seal did not hold so exhaust gas reseumed leaking, but the noise was not as big an issue.

More recently I removed the epoxy -- easily broke it off by hand (proving how ineffective it was) and did the tin can thing, sort of:

* Cut a 1/2" ring from a bean can.
* Coat inner radius with Permatex Copper gasket maker
* Wrap around cracked part of pipe
* Secure with exhaust clamp.

This will likely be a more permanent solution. I say likely because I am now thinking I should have let the Permatex solidify on the 1/2" ring before attaching it to the pipe. I may yet still do that and am preparing one in the likely event that I do.

You epoxy patch lasted a week and you lived with the hole for a year, then recently can patched it?

Have you thought of asking a muffler shop to remove the resonator all together and just keeping the rear muffler? People have done this without affect to emissions and I doubt a smog guy will notice.

EricSilver · #42 07-21-2010, 03:36 PM

Quote:

Originally Posted by pifcat2

You epoxy patch lasted a week and you lived with the hole for a year, then recently can patched it?

Have you thought of asking a muffler shop to remove the resonator all together and just keeping the rear muffler? People have done this without affect to emissions and I doubt a smog guy will notice.

Sure did. The leak did not sound as bad and I did not drive the car very much.

The resonator should not be removed because the engine is tuned to operate with a certain exhaust back-pressure. This becomes immediately evident when a small leak is sealed, i.e., no more upshift delays or doggish performance.

pifcat2 · #43 07-21-2010, 06:15 PM

Quote:

Originally Posted by EricSilver

Sure did. The leak did not sound as bad and I did not drive the car very much.

The resonator should not be removed because the engine is tuned to operate with a certain exhaust back-pressure. This becomes immediately evident when a small leak is sealed, i.e., no more upshift delays or doggish performance.

Where did you hear this? I think the ECU / O2 sensor would compensate. What happens when the muffler and catalytic converter degrades over time? What do you think happens when aftermarket mufflers for W124 with different back pressures are installed? The trans is also tunable for shift points.

EricSilver · #44 07-21-2010, 09:01 PM

Quote:

Originally Posted by pifcat2

Where did you hear this? I think the ECU / O2 sensor would compensate. What happens when the muffler and catalytic converter degrades over time? What do you think happens when aftermarket mufflers for W124 with different back pressures are installed? The trans is also tunable for shift points.

When I asked a tech (Silver Star Motors, Vienna, VA) about possibly eliminating the resonator, he told me that.

I don't know if the cat and muffler degrade to the point where back pressure is affected, but I am sure someone will chime in with that answer.

EricSilver · #45 08-17-2010, 04:21 PM

Following up on this, here is what was true:

You do need thicker metal than a bean can, which is too thin and will deform under the pressure of the exhaust clamp, vibration and exhaust system flexing ( and leak al over again).

I noticed noise from back there about a week ago and replaced the thin metal with a thick, stiff ring of copper cut from a pure copper goblet that was given to me as a gift (that I have no practical use for). Applied the Permatex Copper to it, wrapped it around the pipe, clamped it down and so far, so good.

Nonetheless, I want it re-welded but still have not found a welder but will ask about it when I take the car for inspection.