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Repairing cast iron manifold studs

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PeterK

PeterK

Yoda
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I have a TR4A manifold that someone buggered up part where the four headpipe mounting studs go. The studs have been drilled out crooked and off center, one is very near the edge and all are ovaled out.

So no threads left, holes don't match up with a gasket very well and I'm concered about the one especially that is drilled near the outside edge.

Any way to fix this? I doubt Helicoils could be used because I'd have to drill out so much that there wouldn't be enough strength in the old cast iron left to hold them.
 
How near the edge are we talking about? If there is still 3/16" of sound metal, then I would probably try one of the larger type inserts (Keensert is one brand name, I believe) in that hole and any others that are too badly damaged to take a Helicoil. But you may have to take unusual measures to get it drilled where the stud should be, like maybe use a die grinder on the inboard side of the hole.

Cast iron can be welded successfully, so I'm told. However, every weld I've ever seen on an exhaust manifold has broken again within a few months of service. If you have to go that way, I would try brazing or hard solder instead of weld.
 
Another option, if you can't repair the threads, could be to use bolts through both pieces.
 
Hey Peter,

The fix would be to weld the holes and drill/tap from scratch. To do it right, the manifold has to be heated slowly to red hot and then welded. It then gets cooled slowly. If all goes well, the mainfold is as strong as new. Even with precautions, there is always a (small) chance it will crack...cast iron being cast iron.

As you can tell, you need a really good welder (the man, not the machine), and it will cost a pretty good bit of cash. I'd price a used manifold before I got to involved in repairing yours. I've fixed exactly what you are talking about, but only if it is a pricey or hard to find item.

John
 
I vote for drilling the studs out and just using a regular bolt and nut. Welding cast iron is only good if you never heat the part again, once it get hot the metals will expand at different rates and Crack!

Hondo
 
Peter
Welding cast iron is not that hard with modern nickel alloy stick welding.No pre or post heating is necessary.Filling holes you may have to open top some, especially if its a deep hole.Peening bead is recommended to relive stress,which you ususally do just cleaning the slag.Deep cracks are another story.
I have done lots of still in service cast iron repairs on motorcycle cylindrs,cast iron stoves etc.
Not saying this is the best way to repair your manifold,,but dont be afraid to weld if you find a good welder,or have a DC welding machine and some Ni rod to practice.
Have Fun
Tom
 
I might ..... na I wouldn`t .... anyone that has been around the forum for a while already knows what I would say anyway as we have already had a lengthy discussion on welding cast.
And .... the variables are?
And .... there are no guarantees.
Sigh, if I only had a dollar for every bit of nickle i`v put on castings.
 
You can weld cast iron cold...but there are 2 problems.

First, the weld will shrink and contract within the cooler surrounding metal. That induces stress around the weld and greatly increases the chance of a crack forming...maybe not immediately...maybe never. But the stress induced will always be there till the entire part is re-heated red hot to stabilize it.

Second, the red hot weld is essentially rapid "quenched" by the surrounding cold iron when you stop welding. If you quench iron fast, you get a crystal structure called martensite. The metal turns rock hard...and becomes impossible to drill. Everyone has, at some point, tried to drill martensite. It's the metal that immediately destroys your bit. You fix it by re-heating the entire part to red hot to anneal it, and cool slowly.

Some welders will try to slow quench using a gas torch. It may help, but they are merely moving the thermal stress farther away from the weld...but it's still there.

If you can rig a nut and bolt through the stripped hole, then go for it. It will not hurt anything, or make it any harder to weld later. If it were my manifold, I would price used replacements before I went to the effort to weld it. Any metal can be welded. It is not always worth the effort.
 
Here's a couple of photos. This is a manifold I just purchased because out of the two that I have, one is broken in half, and the other has a crack around the base of the headpipe.

I really doubt that this is worth repairing (just MHO). The hole drilled out at the edge is 1/16" from the edge and the cast is pretty involved with rust. So I doubt there is much strength for bolt through.

So ...
https://home.myfairpoint.net/kentech0822/triumph/4amanifold/DSCN1676.JPG
https://home.myfairpoint.net/kentech0822/triumph/4amanifold/DSCN1679.JPG
https://home.myfairpoint.net/kentech0822/triumph/4amanifold/DSCN1680.JPG
 
PeterK said:
Here's a couple of photos. This is a manifold I just purchased because out of the two that I have, one is broken in half, and the other has a crack around the base of the headpipe.

I really doubt that this is worth repairing (just MHO). The hole drilled out at the edge is 1/16" from the edge and the cast is pretty involved with rust. So I doubt there is much strength for bolt through.
Click to expand...

I think using a bolt through the flange would be fine, it would be compressing the two flanges, and there seems to be plenty of metal there for that. But it looks like the mating surface is really pitted, I don't think you are going to get a very good seal, at least without surfacing it.
 
I would be sending Marv a PM.

Scott
 
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