luckett

I have a crack forming along the weld on the exhaust in front of the cat and was going to put some jb weld on there for a quick/temp. fix. Does anyone know if jb weld will hold up to the high temp. of an exhaust?

Danno

No way JB weld will hold up. What you can do is clean/sand/wire-brush up that area really well and braze over it. If you do a nice even concave fillet joint, it will be a permanent fix. The problem with arc-welding is it creates stress risers (due to physical shape of weld), and weak spots just beyond the weld due to carbon-migration.

luckett

With what filler metal, bronze, silver, alu., some alloy? Melting point of the filler obviously needs to be higher that the exhaust will get.

Alan C.

You could MIG weld the part if you use a 439 or or 409Ti wire. Danno is correct on the carbon issue. The problem lies in the heat affected zone HAZ. The carbon ties up the chrome in the HAZ and thus depletes the chrome from the grain boundaries. Sort of like taking the mortar out of a brick wall. The HAZ is then vulnerable to IG corrosion, not good.

The other issue with carbon I think Danno is hitting on is the fact that it is difficult to properly clean the weld of carbon contaminants.

I have repaired the welds in the past but I have done it with TIG. Drill a small hole about 1/4 in front of and behind the crack. Hopefully this will get you beyound the crack propagation zone. Then take a dremmel tool with a small bit (1/16) and open up the crack. Fill with a 308L wire and it should hold, mine did.

It helps to have a machine shop for a research group at your disposal.

Alan

luckett

I don't have access to a welder and I'm not about throw the exhaust over my shoulder and hop on the bus to the local welder. So what do I braze it with?

Here are some pics of the crack:

PaulStewart

IMHO you have 2 choices: buy a new one, or take it to a good welder. Anything else will fail. This type of problem is usually caused by a loose or missing exhaust hanger.

Danno

Ahh, I see the problem! While there are issues caused with the differences in temperatures inside and outside of the heat-affect-zone, that can be remedied with preparation before and after welding (pre-heating parts and annealing afterwards).

I would surmise that the cause of failure in your case is actually due to the stress-riser that's caused by the thin-walled tubing suddenly transitioning into a thick weld. This high-flex to zero-flex transition could have been relieved by grinding down the weld so that it's smooth and the transition between the two parts is gradual. You ever see the welds on TurboTim's exhaust? The joint is seamless with the weld not even protruding above the surface at all!

Anyway, you can braze that joint closed with brass. Brazing typically uses temperatures around 1500-1700-F so you won't have to worry about the brass melting off. A lot of muffler shops can do brazing but they're typically not very skilled at it. They usually do unshielded arc-welding with flux-coat rods, which doesn't provide the strongest welds anyway (lots of contaminants).

I'd check out some of the custom bike builders like Serrota or Eisentrout in that area. There should be an apprentice or two around that can fix that for you in less than 5-minutes. If you were closer, I'd come over and fix that for you easily.

luckett

Danno,

Have you been sneaking into my garage at night while I'm sleeping again? I happen to have a Serotta and an Eisentraut down there!!!

BTW, Serotta is in upstate NY, not the Bay Area.

Thaddeus

You could apply some kind of custom heat-resistant weatherstripping, one that takes paint...

Thaddeus

luckett

Can you elaborate on this heat resistant weatherstripping? How is it going to bond to the exhaust? Will it take the high temps?

And why would I want to paint it?

luckett

bump