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  #11  
Old 07-30-2006, 11:42 PM
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Quote:
Originally Posted by one_rod
It's been a very long time since I had anything to do with engines like that, but I do seem to remember that at one time ceramic coatings were used on some exhaust parts.

Conventional shot blasting will not touch engineering ceramics, and obviously weld will not stick to it.

As you ground out the crack line there may have been enough clean metal revealed to, just, take the braze metal.

If it is ceramic coated then you really may not be able to trust the integrity of that braze though.



one_rod.
I didn't know that about ceramics being applied. That makes some sense cause when I heated it with the torch it just popped off and the braze did not tin to the surface but the vee I ground it did tin too although not too easily. It is a crappy looking braze but will hold and should not leak too bad.
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  #12  
Old 07-31-2006, 12:41 AM
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Quote:
Is it possible that the major amount of heat cycles that that manifold has been through changed the composition of the iron? Maybe it burned out some carbon or modified some other element in it's make up?

Well, if our engineers had anything to do with the composition it was probably cast from "subliminimal unobtainium".

I found an rv forum member whose daily activity is to keep the "Blue Hair Fleet" or RVs and coaches purring. His advice was to shot peen the manifold after you "zyglo'd" for the unseen cracks and then braze weld. Said the alloy of the cast below the coating was not very friendly to a hi nickel content rod. Of course, he said they replace and will not repair. Doesn't want that kind of repair coming back to the shop.
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  #13  
Old 07-31-2006, 08:26 PM
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Default manifolds

sometimes you luck out welding exhaust manifolds,most times they willnot accept welding or brasing,i think the metal changes somehow,and then when it cracks all that exhaust blows through the crack and makes it worse.
the only ones i try to weld are the ones you cannot buy,sometimes i wrap the crack with steel flatbar and braise it all together.
randy
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  #14  
Old 07-31-2006, 09:38 PM
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Hi,

A friend of mine, who's father was a blacksmith showed me a cool trick for exhaust manifolds, especially ones subjected to very high exhaust temps.

Someone had a cracked one off of a motor home. They taken it to several welding shops to have it welded, but the welds always cracked. He explained that this was due to the repeated very high heating and cooling cycles changing the chemical composition of the cast iron, basically making very brittle.

His solution was to torch weld it with a cast rod (looks kinda like key stock) with a solid copper 12 gage wire wrapped around the od of the rod. He explained that the copper added ductility to the base metal. His repair was was great, and did not re-crack.

I have used this method a few times myself (with a cast flux as he did as well) and it has always worked well.

I'm not sure of yours or a coating or not, but I just thought Id add this. Everyone here as probably seen or done this already.


Jeff
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  #15  
Old 07-31-2006, 09:52 PM
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Thanks for the tip I will have to get some old cast and some cast rod and practice that. Heck I see alot more cast than I do aluminum.
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  #16  
Old 07-31-2006, 10:01 PM
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That's a very good trick z/28. Now where's SFT's tricks bag......?
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  #17  
Old 08-01-2006, 12:07 AM
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Originally Posted by Tom Zachman
Now where's SFT's tricks bag......?
Good idea, Tom. Here's the best I can do for you on short notice.

Tom's Bag of Tricks

Check the Project Index. And don't forget to submit more tricks to add to it as you come across them.
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  #18  
Old 08-01-2006, 12:43 AM
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  #19  
Old 08-02-2006, 08:13 AM
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Default copper?

i have never heard of the copper trick! thats good info. i have welded cast heads with a torch and cast iron rods,we built an oven out of a 55 gal drum,we cut it off at the first bead,cut some holes in the sides for air,put some charcoal in the bottom,put the head in,added more charcoal,lit it up and added some air from the air compressor and waited 6 hours until the head was glowing,we raked the coals off the head,welded the crack,recovered the head with coals and dirt and let it sit a few days.worked out fine.
i don't think its worth the trouble to do this for money,we did it on a bet we could not do it.and i worked with an old guy (rip) that wanted to teach me how to do it.
i do like doing stuff that can't be done,if you know what i mean!
randy
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  #20  
Old 08-03-2006, 04:32 PM
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Heck, if everybody already knows it can be done, what's the point?

Every impossible thing I do brings me one step closer to omnipotence!

:evil:
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