Posted by David Sherman on Saturday, September 10, 2005 at 4:39AM :
In Reply to: Or maybe posted by Dave Speed on Wednesday, September 07, 2005 at 9:18PM :
The threads are in the block, and I personally would not take a torch to a block for any reason. Too much chance of cracking or warping it. I some people successfully weld up a block using a stick welder if the crack is far from the cylinders. To braze up the threads you'd need to get a small section of the exhaust manifold area bright red, while everything around it is cool, which is a recipe for trouble. This is a complicated part of the casting and is in a place where alignments are important. The only way to braze it safely would be to strip the block down to a bare casting, and heat the whole thing red hot, which is far more trouble and more risk than simply putting in a helicoil or a solid thread insert.
I have some inbred bias against helicoils, not based on any bad personal experience, but because I remember my father having some major problem with them on the Minuteman missile, where he was an engineering supervisor (at Boeing). The result of the trouble was a gold-plated helicoil tie tack for my father, and a program edict that "thou shalt never use a helicoil".