390 manifolds cracked

Nigel

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Hi new to the group I have to remove the manifolds which are cracked ,a job I have put off for about 2 years any tips as I’m sure these are going to snap it does look like someone has had a go on a couple of the bolts. I have rebuilt all the front and rear suspension , but now it’s the manifolds time any tips would be great I was told to take the engine out as space is a bit tight thanks Nigel from the UK
 

El Diablo

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After you remove the manifolds, you will need to give them a thorough cleaning. I prefer to use a glass bead cabinet or sand blaster but a good wire wheeling will get the job done. Then use a die grinder with appropriate shape to grind a V in the crack.

As for welding, some prefer to use a TIG welder but not everyone has access to one. I like to use a stick welder to do manifold repairs. Use an oxy acetylene torch with a rose bud tip and medium heat to heat the entire manifold. Don't concentrate the heat at any one spot as it is possible to cause further cracking.

As far as what rod to use, there is a wide variety of cast iron repair rods on the market but only a few that I can trust. The best I have ever used is called "Certanium 707". However I cannot find it anywhere. The next best that I use is "MG-600". You may have to special order it as most welding supply stores don't stock it.
 

nosgood

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Use some PB Blaster or Liquid Wrench on the bolts before you try anything. I'm not sure what you have available in the UK, but any respectable lubricant will help. I took me two nights to remove the manifolds off of my 472. I soaked them in PB Blaster a couple times and they finally loosened up. Good luck!
 

Schurkey

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I've never had good luck welding old exhaust manifolds. If the welds hold at all, they fail within a year or two.

Turns out that the iron castings retain carbon from the exhaust. The iron alloy of "old" manifolds is not the same as when they were new--the carbon content increases, and of course they get a bazillion heat/cold cycles on them. The iron just becomes brittle.

If it were me, I'd braze the cracks, or source headers or other manifolds.
 

8ad-f85

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I worked for one of the largest iron casting welders and would suggest the same.
It's kind of a waste of time or money for something easily replaced.
That and headers have the potential to help so much if mathed out correctly.
 

Preet

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Hi I have a 63 Cadillac with 390 engine can anyone please tell me where to buy new exhaust headers. I tried online lot of places but was unlucky.
 

48Austin

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May want to try CadCo.
 

Caddylackn

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I would try EBAY. Exhaust manifolds without cracks are becoming hen's teeth
 

Bluenotch

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Hi I have a 63 Cadillac with 390 engine can anyone please tell me where to buy new exhaust headers. I tried online lot of places but was unlucky.
I have same issue are the the same as 429 472 500? That one year wierd engine
 

Caddylackn

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The 429 exhaust manifolds could be the same as the '63 390 since it's the same engine family, but I don't know that for a fact.

The 472/500 use four port exhaust manifolds and they definitely don't fit.
The older 49-62 331/365/390 exhaust manifolds may fit, they look similar but I don't know for a fact if they will fit your 390.

I do know that the 429 eldorado exhaust manifolds are different than the other 429 manifolds.
 

Motorfingers

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Cadillac had a number of different engines and models, so I would go by part number in replacing them, if possible. For a restoration, I would look to a recycling yard for exhaust manifolds from a lower mileage car. For a daily driver or a car for normal usage, I would get headers for your specific engine and car from Summit Racing or other aftermarket supplier.
 
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