TR4/4A TR4A exhaust manifold crack story

[AweMan]

Working for the D.O.D. {Govt.} stringent repair proceedures are set fourth by Government Engeneers and MUST be strictly adhered to by anyone involved in the repair/rebuilding of any and ALL vehicle parts.
As I stated, I`v never tried ALL RODS or PROCEEDURES. click here To see an article about Lincoln Ferroweld rod and some cast iron welding proceedures

 

[TR3driver]

Personally, I find exhaust manifolds darn easy to weld up.

That's pretty much what the fellow that welded an Audi manifold for me said. But it cracked again anyway, in just a few thousand miles.

 

[foxtrapper]

That's pretty much what the fellow that welded an Audi manifold for me said. But it cracked again anyway, in just a few thousand miles.

(Shrug) Fear the weld if you wish.

Fact is, it works well when done right. As the many thousands of welded tractor axles and engine blocks attest, in service for year upon year. Things like the fero rod and the like were created just for this sort of repair, and they do it quite well.

 

[TR3driver]

But engine blocks and tractor axles are a lot different than exhaust manifolds. They don't get heated to 1000F on a regular basis.

 

[tomshobby]

I agree that it can be done. I don't think anyone argues that. Is it a sure thing, far from it. I remember when it was popular to make split manifolds for Chevy stove bolt engines using two manifolds. It often turned into a disaster and rarely took only two manifolds when it did work.
I also agree with AweMan that the cost vs success rate makes it a gamble that may not be justified. Just the cost of rod alone can factor in. The rod I used 20 some years ago was over $9 a pound then. But it was some excellent rod.

Would I try repairing it, yes. If it worked great, if not so what.
Would I pay someone else to try it, no. Could easily cost more than manifold is worth.

If I did this I would bevel the crack not more than half way through and fixture the manifold. I would preheat according to the rod manufacturers recommendation. Cold repair is generally for items that cannot be removed or are too large. I would use skip or back-step welds. I would set the amps to the lower recommended range of the rod and probably use AC current because it tends to clean the weld better. And I would peen each bead while it is still hot to relieve stress. And let the manifold to cool slowly. I used to actually apply heat with a torch during cooling if the conditions caused the cooling to be too uneven or too quick.

But, that is only what I would do and I am sure there are better ways.

 

[AweMan]

The critical temp for Grey or ductle cast iron is around 1,400 degrese. Any hotter than this the cast begins precipitation of it`s elements, molecularly chaning the casting into what is known as white cast iron. White cast iron is very brittle due to the lack of carbon and manganeese molecuels. White cast iron is very supseptible to cracking when involved in ANY type of stress situation. This is why it is important NOT to exceede the CRITICAL temprature when welding Ductle or Grey cast iron. When welding a casting, if there are surfaces that need to be machined after the repair, a specific proceedure must be followed. Some casting repair proceedures are NOT considered sutible for machining. When welding a casting, if not done properly applying the weld can easily over reach this critical temprature thus causing the surrounding area to become the dreaded white cast iron.
Supseptible to cracking along the edge of the weldment.
When implementing a weld on ANY material stress is induced NO matter if the weld is applied HOT, COLD, or OTHER WISE. This stress WILL create distortion even if only slightly. A slight stress on white cast is going to mean a crack, if not immediately, eventualy. When reparing ANY casting stress relief is a MUST DO!
This can be accomplished by several methods, Peening the weld immediatly after each application. or Sanding/Grinding the weldment after application. Of course Sanding/grinding method is impracticle on a weldment that is in a deep groove that requires multiple passes to reach the surface. However once the weld is above the surface, Sanding, Grinding the final weld to a finished surface does help to relieve stress on the weldment. Remember, on this deep groove type weld each weld should also be peened after application.
NO matter what type filler rod and or proceedure you choose it is IMPORTANT NOT to go above the critical temp. of 1,400 degrese and follow the choosen proceedure closely.

 

[tomshobby]

Ah, a man with some knowledge of metallurgy. /bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif

 

[AweMan]

Tom:
I try to be as informative as my welding skills allow,
without being too technical. I wouldn`t want to scare anyone away from trying the repairs I describe with technical information that MAY intimidate them away from trying. However when a subject gets discussed like this one has, I feel further information is necessary for the bennefit of the reader. Sometimes I have a tendancy to ramble on and on about a subject concerning welding. Many times covering the same subject matter. But only to clarify or stress an important point concerning a specific process. I do know a LITTLE about metalurgy, Just something you pick up over 30+ years of working different alloys in the trade.
I take that comment as a compliment
Thanks
P.S. If anyone feels I should shorten up my replies let me know and I will try my best.
Kerry

 

[tomshobby]

Kerry, it was meant as a compliment. I admire knowledge, especially when the holder is willing to share it with others.