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Old 24-06-2010, 12:24   #1
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Welding Exhaust Manifold ?

Anyone want to steer me a little in what's involved in a weld repair for an exhaust manifold?
I'm preparing to remove the manifold from my Ford Lehman 6 cyl and get it in to a shop here in La Paz, baja cal. Mexico. It has a leak about an inch in from aft end (in from where the exhaust elbow bolts on) and is leaking only exhaust smoke (no fluid).

Anyone have knowledge or experience with welding in this part of the world? I'm assuming this is cast iron yes? It it possible to affect a repair that will be long lasting?
Geoff Hemwall
Un Mundo (currently La Paz, Mexico)
Los Angeles
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Old 24-06-2010, 13:00   #2
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Not a welder so comments are based on my experience getting parts repaired.

The exhaust manifold is most likely cast iron, probably common grade "gray" iron which is quite brittle. Problem with welding is the localized heating from the welding process can cause cracking due to the stress from expansion of the hot areas. Solution is to preheat the entire piece to minimize the temperature differentials in the part.

I would make sure the welder has experience with cast iron. Does he repair exhaust manifolds in cars? Same issues.
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Old 24-06-2010, 13:03   #3
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perfect. thanks very much skipmac. exactly the kind of guidance i was looking for. love this forum.
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Old 24-06-2010, 13:24   #4
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Hey, don't thank me yet. Let's wait until the real experts weigh in. I could be wrong.
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Old 24-06-2010, 13:47   #5
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okay, and i'll let you know what happens when i get the manifold in front of a mexican 'expert.'
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Old 24-06-2010, 14:02   #6
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If you have doubts about the skills of a Mexican "expert", why not pay ten times the money and take your manifold back to California and have a shop there do it?
90% of the welders in California are Mexican and they are really good at anything they do from farming to restaurant work.
Without them California would grind to a halt in a week.
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Old 24-06-2010, 14:08   #7
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i meant exactly that i'd be taking the manifold to an expert here, in mexico, and i'm sure he'll have something to say about it.
my sailing partner is mexican. i own a business in mexico. i love mexicans!
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Old 24-06-2010, 14:14   #8
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Sorry dude
I've spent the last two years in Louisiana and I've had it up to here with bigots.
I misunderstood you.
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Old 24-06-2010, 14:25   #9
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not a problem. i understand the frustration. i don't like bigots either, but it's always their loss; they're the ones who constantly cheat themselves of knowing the world's best peoples.
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Old 24-06-2010, 15:56   #10
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The problem is a manifold is low grade cast iron to start with heat and salt do not help You can try but if you ask anybody who wasted the time is most probably will have little success best of luck The good news is a new manifold is avaiable
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Old 24-06-2010, 16:12   #11
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okay available is good. it's just that 2500 hurts. think i can do better than that?
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Old 24-06-2010, 16:58   #12
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Yes welding (nodular) cast iron manifolds is tough but the good news is that you should know whether it is successful as soon as it has cooled - if it's going to crack you should be able to see it then: if it's all good then it's unlikely to crack in a few weeks time (other existing weaknesses notwithstanding).

I use NI rods. The biggest issue is keeping the global temperature even across the manifold, so yes the most common way to do that is to heat the whole manifold before welding. VERY important that you then bring the temperature of the whole thing back down SLOWLY. Burying it in a tub of sand has worked better for me than using an oven.

An alternative is to weld it cold but super-slowly (i.e. in small amounts, waiting for it to cool in between each little weld) so the local heat doesn't get too high. Tapping the weld with the round end of a hammer in between each time apparently helps it cool evenly. I have tried this way once (too lazy to get the oven going that day) and it failed, so I'm no expert (and was doing it on second-hand advice so might have got the technique wrong in any case).

With proper heating and SLOW cooling my success rate is probably more like 85% - 90%.
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Old 24-06-2010, 18:24   #13
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weld repaired exhaust manifolds

All the cast iron exhaust manifolds repaired by any means that I have experience with have been very short lived. If the repair allows you to limp to a port where you can replace it with a new one it will have served its purpose but can't be relied on as a permanent solution. The only thing I have gained from weld repaired manifolds was experience. The reason they crack is metal fatigue from heat expansion and contraction and there simply is no way to stop that. I know a fellow with a JBweld patch held in place with a hose clamp who claims it is 4yrs old so I guess there are all sorts of ways to deal with it but that would not be my choice.
Good luck with it. Jesse
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Old 24-06-2010, 18:31   #14
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I recommend brazing it with a torch and flux coated brazing rod. Make sure to clean thoroughly all carbon, oil etc first. This makes a very satisfactory repair if done properly.
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Old 24-06-2010, 21:35   #15
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Jesse & Vintageray,
You guys stand on opposite sides of my dilemma. I don't mind yanking the manifold off and making a best effort to repair it, but I'm afraid of leaving here (relative civilization) and after thinking I've solved the problem, ending up with a cabin filled with carbon monoxide, as was the case coming down from LA whenever I had to run the engine. If I could find a good used manifold I'd jump on it, but that doesn't seem likely here thus far. I probably should get my head around spending the $$ on a new one but ohhh that hurts.
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