I have just discovered the cast iron exhaust manifold on my 230ci flathead six Plymouth is broken. Unfortunately these cars are somewhat akin to hens teeth where I live, so the chances of a replacement are slim. I've done some Googling, and learnt that preheating is necessary before welding, also controlled slow cooling, and it's just as likely to recrack anyway. At this stage of the project I dont really want to build headers, which have questionable benefits on a lowrevving stocker anyway. Has anyone any thoughts or ideas on alternatives to Preheating and brazing or nickelrod welding?
not that hard to prheat if'n you have the right tourch but remember you have to heat the whole unit it should be small enough to put in your oven at as high a heat as posible and there is some cast rods you can use with oxy-acetaleen tourches if you go the brazing route the br*** won't take the paint it seems to never stik and you have to groove the cracks to be welded make sure it's cleen Al
If you have access to a TIG welder and some silicone bronze rods, this way has worked very well for me, if the crack is very long, or all around you might need to stop a few times and let the heat "even out" in the weld...the trick is to not localize the heat too much, just like welding sheet metal. 1) sandblast and clean...needs to be clean as possible. 2) use a grinder to bevel the edges of the crack 3) clean some more with a wire wheel 4) pre-heat in a large oven, or with torch....heat even to 400 deg. 5) weld 6) relieve by using a welding hammer to peen the weld 7) bury it in a big bucket or box of sand...this will let it cool slowly good luck, --reed
V out cracked area. Preheat (gas grill works good). Silcone bronze, cast rod, stainless filler,nickle rod, braze Peen your welds! maintain interp*** temps. SLOW cool - gas grill works geat for this again. Last one I did I let cool by turning it down 50 degrees at a time - every hour or so. FWIW Last time I really wanted to try the cast iron riller rod, but they were crazy expensive (I had to buy something silly like 5 lbs - and I only needed a stick or two) Practice on some junk first - you'll be glad you did!
An old guy I know who has beeen repairing cast iron heads and blocks for years gave me a demo on welding up a manifold. His theory is that brazing on an exhaust manifold is a NO-NO because of the heat cycles the piece has to endure-the iron and the br***/bronze don't expand at the same rates thus leading to cracking. He follows what has already been said : A LOT of preheat followed by welding with castiron rod. The rod is kept in a fairly large puddle as you go. Needless to say, cleaning and joint prep are necessary. Very slow cooling -a day or so packed in vermiculite or surrounded by (horrors) asbestos blocks- is required.
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