Thin lead for sealing exhaust flange leak
 

Not sure what the formal name is for it, but the bell shaped fitting on the northernmost tip of the exhaust line proper where it joins to the exhaust manifold: I have some not small leaking there. When I spray soapy water on that union (cold) and start it up I see copious amounts of gaseous molecules escaping. Too big even to form good bubbles in some spots. I think it's giving up more noise than I want.

I happen to have a quantity of lead sheating, sort of rolled up, it's real close to 1/16th inch thick. Lead melting point: 621 F. I was thinking to come up with a template - I'd use some stiff paper/cardboard, and make a template. It would look a bit like a smile, if about 3/4 wide, and stretched over 10 - 11 inches. That way when you wrap it on the inside of the bell thingy it will all be snug and roughly line up with the leading edge.

The hope is that lead is soft enough so that it will conform to imperfections and seal. I'm only partly optimistic that it will work. It's way softer than steel and softer than brass but that doesn't necessarily mean it will distort and do what I want upon tightening the bolts.

What do you think?

I'd think it will melt away soon enough. My two cents, copper is also soft and has a melting point of 1900f+.

I don't know if the exhaust pipe at that point will melt the lead or not. Seems possible not. The lead would seal that up nicely though I think. It would conform as you are hoping it would I think.

I use Walker Acoustiseal on flange joints. Once the solvent bakes out, what's left is mostly carbon. It's quite effective and easy to remove when the time comes.

I think you should take the joint apart and see what is really wrong there. If it is rusting away, maybe you can patch it up. If the steal is cracking a breaking, you're probably going to have to buy new parts.

Note that the nuts are a copper alloy and are one-time-use, but I've had good luck re-using them on a temporary basis.

Auto parts stores sell exhaust putty that is mostly made of ceramic and is intended for this purpose.

x2, JB weld and other brands are cheap and readily available, made specifically for patching exhaust systems. Lead is nasty stuff, I would not want to be handling it, or melting it and breathing the fumes.

I did wonder about the wisdom of having lead getting hot and not far away from my tender nose. I should have known there'd be a compound designed for the purpose. Would be quicker to use than what I had in mind.

Thanks for the info.

A large thin copper washer might be best, but where to find one? I think muffler sealant is similar to "furnace cement". It is an aqueous solution of fine alumina and other minerals (silicas) which you spread on the joint. I think the water mostly just evaporates, rather than chemically forming bonds as happens with Portland cement (calcium). The leftover powder simply plugs the gap and soot will later fill in any remaining openings. Alumina is aluminum oxide in semi-crystals. Sapphire is the pure crystal form and melts >3000 F. I think fireplace brick has much alumina, which handles higher heat than clay bricks. Silicon oxide is more like glass and melts ~1000 F. Silicone rubbers are good to ~500 F and don't usually last in exhaust systems, even down by the muffler.

Which part of the exhaust system is it that's leaking? Got a photo of the area in question?

Isn't the joint bell-shaped because it's an active connection that takes up movement? You can't use a copper washer or ceramic putty in such a joint. It typically uses a thick ring of special material that looks like steel wool impregnated with other material.