Exaust Manifold Welding Needed

[cwestra]

I was scraping gasket material off my exaust manifold the other day and discovered a crack at one of the flanges.  The piece had obviously been hanging on by a thead for quite some time based on the rust.  Does anyone know who can weld this up without cracking up the rest of the manifold?

[heminut]

You need to find someone who specializes in welding cast iron. The part has to be heated up in an oven or with a rosebud tip on a torch, and then welded with a high nickel rod, or you take a chance of the metal spiderwebbing (cracks).

[cwestra]

That's what I understood needed to be done, as well, however, all of the shops I spoke with say that no longer is the case.  I would hate to take it to someone who's of this opinion (no pre-heating), especiallly if it is incorrect.  Any thoughts from you guys who might have first hand experience with this?

[femtnmax]

I agree 100% with Heminut.  Spider cracking can easily be a big problem.
I have heard of heating the parts prior to welding and still having cracking.  I have heard of cold welding  IE weld a button sized spot, let completely cool, then do another spot, etc. and slowly stitch the whole thing together, though I have not done this method myself.
Any repro or good used ones out there???

[Topcat]

Back in the early nineties I scored on a set of 340 70' exhaust manifolds. One of them had a cracked off piece on the outer inlet. Right where the bolt goes thru. I took it to a welding place in Campbell, CA and they welded it up. They did a nice job, there was no bead and I could barely notice it. I ran it on my 340 I had at the time then for quite a few years without any problems arising.

[heminut]

 I have heard of cold welding  IE weld a button sized spot, let completely cool, then do another spot, etc. and slowly stitch the whole thing together, though I have not done this method myself.

I've got a 392 hemi block that was cracked on one side by the center freeze plug and was cold welded. I saw the engine running an irrigation pump (long story) before I bought it, and it never leaked. I acquired it several years later from another party and instantly recognized it from the weld job. A friend of mine that ran a local automotive machine shop next door to a welding shop told me about how the oldtimer next door had welded the block. He said the old guy would weld a little on it then go work on something else, only welding on the block 2 or 3 times in one day, and it took him several days to get it welded up. It's an ugly looking weld, but I know for a fact it worked.

[dutch]

I`ve welded some of those.  I always heat them in a furnace up to about 500`celcius (  no idea how that would be in fahrenheit.. )   then wrap it in a ceramic blanket to keep warm ,and heat the cracked area further up with a torch till it`s cherry red.  Immediately start welding with special rod for cast iron, but make sure you have had the rods in a oven for at least an hour at 220`C.  These rods absorb a huge amount of moisture from air and you don`t want a wet weldingrod.  weld no more than half an inch at once... the heat in the manifold and welding it will cause your rod to burn.  when you have welded a spot,  brush or hammer off the slag quickly and hammer the weld with a small round top hammer. This will take out the tension from the shrinking weld, and not doing this is why most manifolds will crack again after a while.
Repeat procedure till all welding is done and try to keep a constant temperature.  When done wrap the whole think in a good amount of ceramic blanket and put it back in the furnace ( off ) if possible. Cooling down SLOW... 24 hrs would be nice.
there will always be the risk of new cracks but this should minimize it... good luck