I found a crack in my exhaust =[

I've got a '77 KZ 750 that I just picked up, had a really rusted exhaust, so I started hitting it with a wire grinder to get down to bare metal to paint it. While cleaning it up near the heads I found this:


I know a guy that's been welding for some 30+ years and I'm going to see if he can fill it in with a TIG. I'm just worried about it not coming out clean enough and having trouble getting the collars back in there.

magruder13 wrote: I've got a '77 KZ 750 that I just picked up, had a really rusted exhaust, so I started hitting it with a wire grinder to get down to bare metal to paint it. While cleaning it up near the heads I found this:

I know a guy that's been welding for some 30+ years and I'm going to see if he can fill it in with a TIG. I'm just worried about it not coming out clean enough and having trouble getting the collars back in there.

Get it good and clean and weld it up from the inside. Then a pass with no filler on the outside to fuse the crack at the root. Your weldor friend probably knows this. Oh, and be sure to remove that gasket.

Martin: Thanks for that, I couldn't get it to work for some reason!

Tomw: That's actually not the gasket on the end. The pipe is two layers thick and only the outside one cracked. If you look at the picture, you can see about a half inch down the tube where the inner pipe and outer are spot welded together.

I had a kerker header that did the same thing but it burnt thru both layers before i realized it. I found a guy that said he has a jig he made for repairing the ends.

Powerstroke_fan wrote: I had a kerker header that did the same thing but it burnt thru both layers before i realized it. I found a guy that said he has a jig he made for repairing the ends.

I honestly only realized it since I ground down through a VERY thick layer of rust. Glad I did, pipes are looking good now, just need to fix the bike so I can paint the exhaust and "bake" the paint on.

magruder13 wrote: Martin: Thanks for that, I couldn't get it to work for some reason!

Tomw: That's actually not the gasket on the end. The pipe is two layers thick and only the outside one cracked. If you look at the picture, you can see about a half inch down the tube where the inner pipe and outer are spot welded together.

I wondered about those spots. So how did the flange separate from the pipe? IOW why didn't the inner flange hold it together?

The clamp and split collars press only against the flange. The pipe is otherwise free to pull out and away through the split collars and clamp (and will readily do so without the flange).

Think of it as if the flange was glued to the end of the header pipe instead of being welded, and the header otherwise installed normally. It would be relatively easy to pull the pipe free by breaking the glue bond. While the flange itself will remain held tightly in position by the clamp and split collars.





Good Fortune!

Patton wrote: The clamp and split collars press only against the flange. The pipe is otherwise free to pull out and away through the split collars and clamp (and will readily do so without the flange).

Think of it as if the flange was glued to the end of the header pipe instead of being welded, and the header otherwise installed normally. It would be relatively easy to pull the pipe free by breaking the glue bond. While the flange itself will remain held tightly in position by the clamp and split collars.

I know how the pipe is held on to the head. I've R&R'd them numerous times. It's apparent then that the spot or rosette welds holding the inner pipe to the outer are not all holding.