Manifold Repair

Here's why mig fails on so many cast iron parts, and high-nickel filler does not.

When you heat steel up to red-hot or higher temperatures, it undergoes phase change. Not just solid to liquid, but also bainite, martensite, and some others. These phases are basically re-arragement of the atomic structure and covered by this horrid little diagram.


You can see this in real life when you heat up a steel wire strung between two points. It'll droop. Remove the heat and as it cools it'll shrink, and tighten back up, then droop some more (phase change), and then tighten back up again.

Why all the metallurgy?

The problem is that this phase change occurs in the weld bead when you lay a steel weld bead in cast iron, which doesn't experience the same thing. Since they're expanding and contracting at different rates, re-cracking is highly likely to occur and it usually cracks right next to the weld, as soon as it cools. Especially with low-grade cast iron or iron with lots of graphite in it.

High-nickel content filler metals (nickel brazing, too) don't experience the phase change, and so the chances of cracking are FAR less.

Being that is a low stress part with little carbon, I think brazing would work but the ear will see a lot of pushing and pulling as the manifold heats and cools. The other option is that you can also use stainless fillers with a TIG (or MIG) welder. I've used this to a great degree of success in the past, and it's super easy to do. It lays in very easily. When I first heard this I thought 'BS', but a guy I worked with broke his antique cast-iron Ford wrench which sees a LOT of force. I tig'd with 316 filler and he's using it to this day.

Any welding shop that does TIG will have stainless filler since that's the preferred method for stainless work.

Edit: this is just how I understand it, and the odds of the understanding....pretty slim.

But you can use stainless to weld cast.

halfafish said:

I had some extremely rusty/nasty parts to deal with. I used a 10:1 mix of water to molasses and let the stuff soak for a few weeks. They came out very nicely, and it cost me less than a dollar.

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I've never heard molasses before, I'm picking up a bunch if vinegar on my way home today and a tub for these and am going to let them soak while I wait to see if my uncle finds someone who welds cast before I try it myself.

jos51700 said:

Here's why mig fails on so many cast iron parts, and high-nickel filler does not.

When you heat steel up to red-hot or higher temperatures, it undergoes phase change. Not just solid to liquid, but also bainite, martensite, and some others. These phases are basically re-arragement of the atomic structure and covered by this horrid little diagram.
View attachment 1715401417

You can see this in real life when you heat up a steel wire strung between two points. It'll droop. Remove the heat and as it cools it'll shrink, and tighten back up, then droop some more (phase change), and then tighten back up again.

Why all the metallurgy?

The problem is that this phase change occurs in the weld bead when you lay a steel weld bead in cast iron, which doesn't experience the same thing. Since they're expanding and contracting at different rates, re-cracking is highly likely to occur and it usually cracks right next to the weld, as soon as it cools. Especially with low-grade cast iron or iron with lots of graphite in it.

High-nickel content filler metals (nickel brazing, too) don't experience the phase change, and so the chances of cracking are FAR less.

Being that is a low stress part with little carbon, I think brazing would work but the ear will see a lot of pushing and pulling as the manifold heats and cools. The other option is that you can also use stainless fillers with a TIG (or MIG) welder. I've used this to a great degree of success in the past, and it's super easy to do. It lays in very easily. When I first heard this I thought 'BS', but a guy I worked with broke his antique cast-iron Ford wrench which sees a LOT of force. I tig'd with 316 filler and he's using it to this day.

Any welding shop that does TIG will have stainless filler since that's the preferred method for stainless work.

Edit: this is just how I understand it, and the odds of the understanding....pretty slim.

But you can use stainless to weld cast.

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Here I was in dental school thinking I was finally done with general chemistry and organic chemistry .

Manifold de-rusting process started. 7 gallons of vinegar with 4 gallons of water. I'll let them soak for a bit

I had some repairs to be done to my '69 Abody 440 manifolds (hens teeth parts), so I didn't want to take any chances. I sent them to a repair shop that specializes in cast iron welding. He did a fantastic job. His name is Jeff Perkins and is located near Indianapolis (He worked for many years at Indy Cylinder Head). The shop name is; Perkins Repair Service

DentalDart said:

Thanks! Im going to try and get those muggy sticks and take them to my uncle's shop one day.

Maybe they'd be able to mill it, sand blast it and powder coat it all there too. I know his company does all those things, so we will see what he says.

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Not even "high temp" powder coating will withstand the temps those exhaust manifolds will dish out, especially right at the heads. You're better off with a high temp ceramic coating instead.

I had manifolds "ceramic" coated by a shop that has been around forever. They put special coatings on aircraft parts, race car parts, military, anything you can imagine. I told him I wanted them to look like new cast iron. "No problem, we do it all the time", the owner said. Well they did look great, just like brand new sparkly cast iron. But it was a matte finish, and therefore porous. So the moisture could still get to that rust-prone cast iron underneath. And after a while, the rust came thru in spots. Moral to the story is do not get a matte/flat ceramic coating. Make sure it is glossy and therefore has what I'd call a "sealed membrane" on it.

I am going to pull the manifolds out today and see how they are looking.

I'll look for a ceramic coating to finish them with. I'm loving how the car is sounding with the exhaust and headers so idk if I'll even be using the manifolds. I may change out the mufflers to either a pypes or a super 10, give the car a little more throaty sound before u put the cam in .

DentalDart said:

I am going to pull the manifolds out today and see how they are looking.

I'll look for a ceramic coating to finish them with. I'm loving how the car is sounding with the exhaust and headers so idk if I'll even be using the manifolds. I may change out the mufflers to either a pypes or a super 10, give the car a little more throaty sound before u put the cam in .

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Try POR-15 manifold dressing it works awesome. I did mine almost 2 years ago and they still look great. The 8oz can is more than enough. Sand blast and prep sol then brush it on.

POR-15 High Temp High Heat Resistant Paint

So the manifolds looks great! After like 1.5wks in 7 parts vinegar and 3 parts water. A little 800 grit sanding and here's the result. I'll probably use a little sand paper on them tomorrow after they dry out for the night.

I did something dumb though.... Poured the tub out in the street.... Well now we have rust water stains all the way through the neighborhood. I wonder if my wife or the HOA is going to be more pissed

I'll probably grab a cheap broom and walk through the neighborhood with vinegar and water tomorrow to try and clean a little bit of it up.

They look pretty good, but there is still too much rust on there to put any kind of coating over it. Any rust is too much!

69_340_GTS said:

They look pretty good, but there is still too much rust on there to put any kind of coating over it. Any rust is too much!

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Yea I'm going to do a little sanding on them. The faces where they mount to the block and a couple other spots were pretty soft and I didn't want to keep messing with them until they dried up a bit .

69_340_GTS said:

There's a 98% chance that the sealing surfaces are warped. Even on the manifolds that are not cracked. If you put warped manifolds back on, they usually crack because cast iron isn't exactly very flexible. So any exhaust manifold you want to re-use should at least be fly-cut (milled) flat.

When you get the ear welded back on, the bolt hole will need reaming out and the entire face will need to be milled.

And no, J-B weld won't work.

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Tricky with the drivers side 340 manifold, the outlet sticks out further than the flange..

Update

Still haven't done anything with these since I took them out of the vinegar. They are just sitting collecting dust right now and will probably collect tons of dust over their lifetime as idk if I will use them.
I've been busy cleaning and redinishing my wheels, brakes and axle. Hopefully I'll have it all put together in the next couple of days and maybe the install this weekend?

MOPAROFFICIAL said:

Tricky with the drivers side 340 manifold, the outlet sticks out further than the flange..

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Oh yeah, my machinist did complain a bit about that. But he got it done.

DentalDart said:

Thanks! Im going to try and get those muggy sticks and take them to my uncle's shop one day.

Maybe they'd be able to mill it, sand blast it and powder coat it all there too. I know his company does all those things, so we will see what he says.

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Honestly. Moparmike has explained what needs to be done - so find a shop with an oven or equivalent for this type of cast iron repair.

MoparMike1974 said:

V out the crack, drill crack stops at each end, pre-heat part then weld with nickel rod. Cover part with sand so it can cool slowly. This is the old tried and true method for cast.
However, like mentioned here mig can repair cast well. It really depends on if its a high stress part. The problem with a manifold is they are thin and they expand and contract all the time.

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If its for your own use and are OK with using gaskets well OK. But IMO, its worth checking the face on a spare head or super flat surface. Then if needed find someone to mill or lap it.

For coating, especially since not every little rust pit has been cleaned, might try a non-paint cast iron 'sealant' like Eastwood and Bill Hirsch sell. Supposed to make touch up easier.
When I've painted 340 exhaust manifolds after sandblasting, I used Bill Hirsch's exhaust manifold paint. It last decently but eventually spekles of rust come through -especially near the heads. This was on a car that was sometimes used every day, along with some track time etc.