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

EricSilver · #1 08-19-2009, 10:58 AM

I lost an exhaust hangar which caused my exhaust pipe to flex over and over, and a crack occurred just ahead of the center muffler/resonator.

It is cracked at the weld but not rusted through, so I would think it can be welded.

Black residue on bottom/front of resonator is blown-back oil from a timing cover leak.

EricSilver · #2 08-19-2009, 11:01 AM

Photo Did not Attach in First message. Here it is.

865sp300e · #3 08-19-2009, 12:18 PM

Mine developed a similar crack and the local indy muffler shop welded it for $20.

EricSilver · #4 08-19-2009, 12:48 PM

Great -- thanks.

I am finding the muffler shops are saying "replace," whereas indy repair shops and independent welders are saying they can probably re-weld it.

babymog · #5 08-19-2009, 09:33 PM

All depends on how thick the remaining metal is, ... usually it'll burn through quickly if it's rusted thin and thus can't be welded.

emerydc8 · #6 08-19-2009, 09:39 PM

I have used PC-7 to patch the same spot on my exhaust. It works very well.

EricSilver · #7 08-19-2009, 10:14 PM

Quote:

Originally Posted by emerydc8

I have used PC-7 to patch the same spot on my exhaust. It works very well.

I had not heard of that -- but just Googled it.

If I am unable to get it welded I will use that or Permatex Metal repair epoxy, and then secure a thin pipe clamp over it to keep it from blowing out.

The muffler is only a few years old, is a genuine MB part, and I cannot come to terms with throwing away something that is perfectly good.

I also saw that both tailpipe hangars are broken, as if cut. Considering the thickness of the rubber, I am having a hard time accepting that the weight of the muffler could have broken both of them -- or is that common?

EricSilver · #8 08-19-2009, 09:55 PM

Quote:

Originally Posted by babymog

All depends on how thick the remaining metal is, ... usually it'll burn through quickly if it's rusted thin and thus can't be welded.

Metal thinness was the concern of an indy boiler welder who I asked about it, and may be able to help. But tomorrow morning I will be taking it to a local Chevron station that does welding, and who believe they can fix it. If they can, I will let them.

mpolli · #9 08-19-2009, 10:06 PM

Welding is a weird science. It could depend on the alloy(s) there.

You might post that photo on http://weldingweb.com and see what the alchemists there say. You could post under General Welding Questions or Mechanic's Park.

EricSilver · #10 08-19-2009, 10:30 PM

Quote:

Originally Posted by mpolli

Welding is a weird science. It could depend on the alloy(s) there.

You might post that photo on http://weldingweb.com and see what the alchemists there say. You could post under General Welding Questions or Mechanic's Park.

Thanks!

emerydc8 · #11 08-19-2009, 10:44 PM

The PC-7 works without any clamps. It is like silly putty when you mix it and you can work it into the cracked area enough so it grips really well. Let it dry overnight if you end up using it. It will probably be stronger where you repaired it than the rest of your exhaust.

Kestas · #12 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 · #13 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 · #14 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 · #15 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.