Repairing Thread in Cast Iron

I have a transmission case that someone has brought me and one of the bolt holes has a chuck broken out of it where the access cover bolts to
the case. The case is cast iron and still has about 50% of the thread left for engagement.
Is there a way to cover a bolt of the proper thread with carbon soot from an oxy-acet torch and then screw it into the hole and then braze over the bolt to form a new bore wall and thread form? I have seen this done on aluminum but never on cast iron. Would a nickel filler rod work here? I of course need to be able to get the bolt out and that was the reason for coating the bolt with the soot. My concern is that the high temp will boil off the soot or if a flux is used it will float it to the top and the bolt will be brazed into the bore.
I have mig, tig, and oxy-acet all available.
Any suggestion apprciated.
Thanks, Steve
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Don't know the exact situation, but you may be better off "replacing the bolt hole" by cutting out the remaining piece, then making an entirely new piece with bolt hole/threads and brazing/welding that into place to replace the original "hole". Ken.
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I am partial to epoxy type repairs in cases like this. I often epoxy a stud in and use a nut on it. I do this because of risk to damage to the cast iron but if you want it welded or brazed you could just redrill and tap the hole in either brass or nickel. Saving the existing thread would probably require using a jig to accurately guide the drill and to feed the tap.
I do not know if the soot will permit the bolt to be removed or if it would be possible to form the threads around the bolt during welding. I have wondered if using a carbon or copper plug with threads would work. Maybe someone with experience in this method will let us both know.
Don Young
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On 15 Jul 2006 18:49:34 -0700, " snipped-for-privacy@aol.com"

Much as I do enjoy welding/brazing challenges, this sounds like a job for a heli-coil repair. It's exactly what they're designed to do and they do it well.
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I'm not exactly sure from the OP's post, but it *sounds* like the bolt hole is located in an "ear" or "tab" sticking out from the main casting and that 1/2 of the tab is broken off so that there is only 1/2 of the threads still in the tab and that he wants to place a bolt in the remaining threads and build-up the missing portion of the tab. Of course helicoil won't work in a situation like this.... Ken.
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On Sun, 16 Jul 2006 13:32:38 GMT, Ken Sterling (Ken Sterling) wrote:

No, not if half of the hole is missing.
I have built up weld over a mandrel in cast aluminum. This works because the molten aluminum doesn't fuse to steel. About the only thing I can think of that might work with cast iron might be a ceramic plug. I'd just build up a whole new ear, then drill it and tap it.
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You will need to need to weld in a oversize mild-steel plug with 99%Ni-Rod. And make sure its plenty oversize so when you drill and tap you will be doing it entirely within the steel. After welding, that cast-iron gonna be hard-hard-hard and will break your tap.
Tony

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