porosity fix for long tube manifolds

[mkolden]

I developed a crack in my long tube 427 manifold on the inside of the passenger side piece.  I cleaned it up, gouged it out, and drilled the ends of the crack.  I then heated it up and welded it with stainless wire.  everything looks good after grinding and sanding the weld down but when I put dawn dish soap on it and run an airline down inside the header, I have a ton of porosity around the welded area.  Is there a ceramic or other coating that would work for this?  I am thinking Cerekote.  Any other suggestions?  Thanks

[cjshaker]

Brazing should do a good job. I don't think ceramic coatings would hold up for filling porosity holes.

[Dumpling]

Curious, would an all-over outside ceramic coating, seal a set of porous headers? Or would the ceramic coating be weakened and ultimately fail due to the underlying porosity?

[gdaddy01]

why use stainless wire ? I would think a similar metal would be better to weld with .

[Henrysnephew]

A picture of your repair would help BUT I'm betting that your porosity issue will "heal" itself, as the manifold interior will carbon-coat and seal the porosity soon after being put into use.  JMO.  Randy M

[Heo]

Braze over the pores or if they are few centerpunch beside them so
they be squished closed

[RustyCrankshaft]

I developed a crack in my long tube 427 manifold on the inside of the passenger side piece.  I cleaned it up, gouged it out, and drilled the ends of the crack.  I then heated it up and welded it with stainless wire.  everything looks good after grinding and sanding the weld down but when I put dawn dish soap on it and run an airline down inside the header, I have a ton of porosity around the welded area.  Is there a ceramic or other coating that would work for this?  I am thinking Cerekote.  Any other suggestions?  Thanks

I would stick weld that. I've done a LOT of old JD tractor cylinders (they're a OEM cylinder with no modern direct replacement) and have had good luck with no leaks. Pre-heat, stick weld with a good high nickel rod (stainless rod is fine or another high nickel alloy rod), post-heat to cool it slowly and then peen it gently. No porosity and likely to not re-crack if you also drill each end like you mentioned you did.

I have not had good luck trying to use stainless wire and mig weld cast iron, especially exhaust manifolds/headers as they have a lot of carbon and other "dirt" in them from the exhaust gases.

[C6AE]

I realize it is late, but I always use a a nickel/iron alloy mig wire to repair cast iron.
Years ago I used sticks, but the wire is so much cleaner and precise.
Like any cast iron work you need preheat and a slow cooling period, but nothing ridiculous.
Fastenal has two pound spools. It is free machining, after the fact.
https://www.fastenal.com/products/details/0857244

I have also a set-up for thermal spray using a special torch with "cast iron welding powder" (mostly nickel) and it works better on exhaust manifolds than any other process I have used yet. It is pretty slick, without any real concern for contamination. If you haven't seen this process you should! (We also use it with Tungsten powder for hard facing)
Preheat and post heat w/slow cooling again are critical. You don't want the part to drop below 650°f while doing the work. Search for> "spray welding torch"
 eBay has the best prices maybe.