Cast Iron manifold for chevy straight 6 , 1978

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I have noted a small crack in the exhaust manifold of my chevy straight 6 engine , about 3-4 inches total. Thought I would make the repair with a 3/32 99% nickel NI  rod stick weld. Some say to braze it but I thought I had always heard not to braze exhaust systems due to the constant heating and cooling. The part is removed from the integral head and on the bench for better access.  Anybody have a better procedure of filler material that is more modern that I don't know about. Of course the proper preheating and slow cool down will apply but I don't have a lot of cast experience. Also some say these are a gray cast, and some say they are nodular iron. Anyone know for sure. I figure to keep temps form 4-500 and make small welds about and inch at a time and let cool back to preheat temp and peen beads just after welding. Any input welcome . Thanks"Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:However you do it clamp the manifold down solid on the face that mates w/ the head. Otherwise you might end up w/ more leaks the gaskets can't fill. I used brass making split manifolds for straight sixes as a kid. Never had any problems w/ it.                                    MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:Are you tiggin it?
Reply:Originally Posted by mla2ofusHowever you do it clamp the manifold down solid on the face that mates w/ the head. Otherwise you might end up w/ more leaks the gaskets can't fill. I used brass making split manifolds for straight sixes as a kid. Never had any problems w/ it.                                    Mike
Reply:I have a tig but have never taken it to cast iron, seems like a good way to keep the heat down. any suggestions on a filler rod."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:I suggest shooting castweld a PM for his input if he doesn't reply to your thread.I can't remember what it is but I recall reading (I believe in one of Peter's posts?) that a cast exhaust manifold looses some of one of the metals "ingredients" (nickel?) due to the constant heating that affects how a crack can/should be repaired.  But I don't recall the details which is why I suggest you shoot him a PM on the matter.If you can't preheat and maintain a proper welding temperature and then assure a proper cool down, he may just suggest "cold welding" (weld 1/2" and let cool enough to touch with bare hand) with a nickel rod but I'm just guessing.  I would also think machining to true the mating surfaces would be required following a significant preheat, weld and post weld cool down.Last edited by duaneb55; 06-27-2011 at 10:44 PM.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:I have mended quite a few just by cleaning them up with a grinding stone where I was going to weld, then welding with Ni 99, in small welds and letting it cool in between.