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On a diesel tractor, the exhaust manifold has developed two holes, possibly from thin castings, and possibly from rust. The manifold is cast iron, and I would like to patch it. A local farmer tried high temperature epoxy. That lasted until the manifold got real hot when plowing.

So I am thinking brazing. Specifically, I am thinking of putting a nickle/copper patch in place (a part of a nickle coin) and brazing it in place with bronze brazing rod, using an oxyacetylene torch. Preheating to 400F and then post heat at 400F, with a gradual cooldown to minimize the possibility of cracking.

Has anyone tried anything like this? Suggestions?

  • A follow-up. The casting was cracked through 80% and very thin. I managed to find one at a scrap yard, so it is installed. They are priced like gold, so I will still attempt to braze. HOWEVER, Stainless steel has a similar coefficient of thermal expansion as cast iron, so I will likely use a stainless steel table knife (the older kind) to make a wrap around patch, unless I can find some 18 ga or so stainless. Thanks for reading, and to @dlu for his comments. Will post an update as appropriate. – mongo Aug 1 '17 at 22:49
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I've had success brazing cracks in castings, but haven't tried patching them like you suggest. But it seems like it should work…

All we did by way of pre- and post-heat was to warm the part overall with a rosebud, and then let it cool slowly after brazing.

It certainly seems worth a try.

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I made the repair as follows: -blasted the manifold casting -shaped a "nickle" to fit over the hole (the coin is mostly copper) -heated manifold in a household over to 400F -used bronze braze to attach the trimmed coin to the manifold -replaced manifold in oven, and baked for 2 hours, then let the temperature drop over several hours

Since then, about 80 hours of time on the tractor, including some high power operation (dragging logs uphill). Repair appears secure, and my ears thank me.

If anything adverse happens, I will repost comments on this repair.

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