Rebuilding broken thread bore 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

Reply to
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That would be possible, I cast brass for a special half-nut over a one inch steel rod with a modified acme thread using lock-lube graphite powder to keep it from sticking. It would probably be a lot easier and faster to just braze it up and re-drill and tap.

Reply to
Stupendous Man

I've done this quite successfully in the past by using a carbon rod (artist's solid graphite pencil) to plug the hole, welding it crudely around, then drilling and tapping for a Helicoil insert. It's easier than trying to cast a thread!

Reply to
Andy Dingley

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