Yeah, I probably don't know what I'm doing with an arc welder.  But I fixed the muffler, and it works now.  Git 'er done!

  2016 Aug.     Tech   Metal & Shop


Suppose you've got a muffler where the end is broken.  It's at that sheet metal cone that joins the inner pipe with the outer casing.  The result is a major exhaust leak.  It's so bad you can't patch it with that muffler putty.

But it just so happens you know how to arc-weld.... sort of.


A new muffler could be a hundred dollars or more, and you really don't want to throw this one away.

Let's talk about how you "might" weld a muffler with 6011 at ninety amps. 

Reader-Supported Site

This website is made possible only with the support of readers like you, when you use the links on here to purchase your gear. 

If you want to see welds that aren't nearly as awful, check out some of the other articles on this site.

In This Article

The Muffler

An Idea

6011 At Ninety Amps

6013 Attempt

Slaggy Welds, Now What?

7018 Welds


The Muffler

This muffler starts out in really bad shape.  The sheet metal is separated at one end.  And it's bent inward.  Someone hit a low branch!

You try to bend the sheet metal, but it won't budge.  You don't have any sheet metal, so you can't make a patch for it.

That means you can't really braze it.

The huge gap means you can't MIG weld it, even if you had a MIG welder.

So you've got this muffler that's sort of junk, but it might be salvageable.  Possibly. 

An Idea

What if you could do some ridiculously over-the-top repair, such as... oh, I don't know... rebuilding the entire end of the muffler with weld.... ?

You know those sites where experienced welders look at photos of ugly welds, and laugh? 

Well, those kinds of ugly weld photos begin with ideas like these.

6011 at Ninety Amps

So let's suppose you decide to try building a whole new muffler-end with 6011 weld.  You choose 6011 because (A.) you don't have all day to grind metal down to clean surfaces, and (B.) 6011 is a good electrode for gap bridging. 

But there's, uh, that one little problem with 6011... it doesn't get along with sheet metal. 

And yet, there is a way that it can work.

Let's make sure everyone understands... use this technique only if the muffler would probably be scrap anyway.  Also, I probably wouldn't use this method on a muffler for a road vehicle.  (Disclaimer.)

Let's say the sheet metal separation is at one end of the muffler, where a cone of sheet metal joins the header pipe with the cylindrical outer casing of the muffler.   There are basically two weld seams here.  First there's the one that connects the header pipe to the sheet-metal cone.  Let's call that the inner weld.  Then there's the weld that connects the sheet metal cone to the outer shroud.  Let's call that the outer weld.

I found it was possible to build up dams of 6011 weld from the inner weld to the outer weld.  Basically it bridges the gap that used to be occupied by sheet metal.

The idea is to avoid destroying what sheet metal remains there.  Keep the electrode away from the sheet metal, but just close enough that the weld can form a bond to it.  You might be able to do the whole job without welding directly to sheet metal, but if you accidentally perforate it, you'll have to repair it.  And if that happens, try that technique:  keep the puddle closer to the existing welds, but let it melt onto the sheet metal.

It's kind of tricky.  You want the molten weld metal to be hot, but not so hot that it eats up the sheet metal and leaves holes in the muffler.  And as I said, you might be able to do this technique without ever having to weld to the sheet metal.  It depends on how the sheet metal has separated, and how extensively.

Table of Contents


6013 Attempt

6013 was really intended for nice, neat, linear welds.  Using it for gap-filling results in a lot of slag in the weld. 

(I should have known this, but I wanted to find some reason to use up the multi-pound box of 6013 that I'd bought a while ago...)

By the way, I think the 6013 was run at 105 amps.

Table of Contents

Slaggy Welds, Now What?

Once cooled, the result looks kind of rough.  It looks like it will probably hold... but the slag!!  And the uneven surfaces!  It looks like amateur-hour at the welding school.  Hey, I didn't say I was a great welder.

So you think that photo at the top of the page looks bad?  No.  You didn't even see the welds before that.  They were so ugly, I don't even think I wasted a photograph on it.  Did you ever see one of those really gnarly old burl trees?  They looked like that.

Normally you don't want slag in the welds.  Even if the welds are somewhat strong, it just looks awful.  I think slag probably accelerates the rusting of welds, too.

A muffler doesn't have to support nineteen tons or anything like that.  It also doesn't have to look nice.  People plug leaks all the time with muffler putty, which is not even as strong as a slaggy weld.

And besides, there's one more step to this little project.

Shop For A Nice New Welder

Table of Contents

7018 Welds

If you do arc welding much, you probably noted that the welds in the photo look like 7018.  Ugly 7018, but still recognizable I think. 

Well, if you were welding on top of the awful, slaggy moon-scape that I already set down with 6011 and 6013, your welds might look like that too.  That's what happens when you have to keep the electrode moving fast, so you don't wreck the sheet metal on the muffler.

With some grinding and a lot of slag-chipping in the pock marks, I prepped the 6011 / 6013 surface... I mean, surfaces... into something that would probably take 7018 welds.  And it did.

The idea was to weld on top of existing welds, because they didn't melt as easily as the thin sheet steel.

By this stage I tried moving the electrode slowly, keeping it up against the weld puddle, etc.  You can see the welds look pretty awful, but they at least sort of look like welds.

I used 105 amps with 1/8" 7018, I think.  If I did this project today, the beads might look straighter... but seriously, who cares?  The singular goal of this whole exercise was to get a muffler into working condition again.  And for that, it worked.

Shop For A Nice New Welder and please, learn to make better welds than I did here.

Table of Contents


It's possible to weld a muffler successfully with too big an electrode, and too much current for sheet metal.  It might not be ideal, it might not even be correct... but it's possible.

If you go this route, you'll want to keep the weld puddle closer to the existing weld seams.  Let it run onto the sheet metal a short ways as you go.  What worked for me was to build up dams of cooled 6011 weld, starting on the header pipe weld seam and moving outward to the weld that joins the sheet-metal cone with the cylindrical part of the muffler casing.

In case you need to weld directly to sheet metal, it really helps if you have a welder that lets you dial the current way down.  Then you can use 1/16" or 5/64" rods. 

Remember, I never said this technique was ideal, and there are no guarantees.  Someone with more resources and time would probably fab up a new sheet-metal cone, then MIG weld it.  That would probably be the right way to do this.  But, if you're curious as to how someone might weld a muffler with 1/8" 6011, hypothetically.... there ya go. 

I hope this article was helpful or at least entertaining;  if so, please help me out by using the links on here to purchase any of your stuff.  It helps me keep this website on-line and bringing you helpful articles like this one. Thank you in advance.


Contact me:

3 p o.t o . 1 2 0 s t u d i o.. c o m

This won't directly copy and paste.  Please manually type it into your mail program.
No spaces between letters.

Home Page

Site Map

What's New!


Copyright 2016


Back to Top of Page