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MG MGB Technical - Can I have My Exhaust Manifold Welded?

I sent my stock 71 B exhaust manifold to Jet Hot for treatment last week. They called on Friday and told me that, after bead blasting it, they found a very small hole in the front branch pipe. It looks like the hole resulted from an air bubble that may have been present during the casting process.

The hole on the interior is the size of a pin hole - the outer side hole is about the size of a BB or pellet.

Can this be properly repaired with a simple weld.

Is welding cast iron possible in this instance.

Any suggestions. I could just buy a second hand manifold and go with that - but thought I would double check before doing that.

Thanks in advance,

Jeff
Jeff Delk

Working slowly and using a nickle rod will provide an excellent weld. Simply don't allow the weld to burn thru, and do one small bead at a time.

warmly,
dave
Dave Braun

Welding this defect in your manifold should be no problem for an experienced welder with the proper equipment. I've welded up a burned out RB MGB single carb manifold years ago on my daughters car. Use oxy-acetilene equipment with cast iron rod (it looks like molten cast iron was poured in a narrow trough to make this rod) with the apropriate flux. Good luck. Mike
jm wenzel

Yep. Brass also works well. I had to fix a stripped exhaust manifold bolt. USed a brass filler and my O/A touch to fill it, then redrilled and tapped it.
Bruce Cunha

Couldn't you just us some JB Weld to plug the hole.

Ste
Ste Brown

I'm pretty sure that was your Iris Blue at the NEC last weekend, Ste. Didn't realise until comparing a photo I took of the OD relay and vacuum switch with one I already had to see which was best and found it was effectively the same photo from the same angle as one you sent me a while ago.
PaulH Solihull

Paul

I heard that former glory has it know but from the pictures it's either really mucky or he has let it go a bit.
Reg number is 1143pf

Ste
Ste Brown

I did think it was in a place that made me think it might have been for sale, but didn't like to say that before!
PaulH Solihull

Jeff.. Just a spot of brazing on the defect. Five minutes wit5h a brazing torch and all will be well.
darnoc31

I hope I'm not hijacking this thread too much but I have a question: Does brazing work with the water jackets on cast iron cylinder heads? The water jacket isn't as highly stressed as the combustion chambers so it might be a solution...

I've heard that welding cast iron heads is possible but fiendishly complicated.
Mike Standring

I think it was Fletcher Millmore who said that brazing can cause cracking in steel panels - maybe it could also in castings?
Art Pearse

Although, I looked up brazing, or How to, and found a site that certainly condoned it for steel bike frames etc. But I agree, what about brazing a casting? I think it will be important as Stephen Strange has said that matching coefficients, then heating the parts well, and allowing natural cooling will govern success or failure. Perhaps letting the specialist do the job is best? Mike
J.M. Doust

Lots of issues with either brazing or welding CI.t5rrrrrrrrrrrrrrrrrrr <cat on keyboard!

Arc gets a local area very hot, so it cools very quickly, producing white iron, very brittle and extremely hard. Prone to cracks. Nickle rod is used for this to produce very ductile welds, which are machinable and (you hope) absorb some of the stresses that lead to cracks. Might be good for this app, as distortion should be very low.

True CI welding amounts to a recast, so you heat the whole thing as hot as possible, weld with torch and CI rod+flux, cool very slowly, and pray nothing distorts too much.

Brazing is a sort of midway approach. Heat the casting as much as possible, braze, cool slowly. Works very well on protuberances like manifold ears, but is tricky on places in the middle of castings like water jackets. It all depends on how the casting expands/contracts. One problem is that CI has free carbon flakes in it, which prevents the filler from adhering; oil soaked castings give a similar result. Generally the joint is ground to give a wide area for the brass to stick to, the whole is heated and "washed" with excess oxy flame to burn off the surface carbon, and you rely on the flux to remove oxidised iron from the injury. Good brazed repairs are generally 1/2-3/4" wide.


I've successfully done all of these, but there is nothing quite as discouraging as the fatal "TINK" while it is cooling!

FRM
FR Millmore

My view of this---
The hole in Jeff's manifold is that small that it will take a split second to weld up

I'd be bolting the manifold up to a spare head if you have one , give it a light touch with a grinder just to clean the place to be welded, then get the electric welder with a nickel rod or if you are going to the welding shop they will probably have a suitable wire for their Mig. and zap it, then lightly peen it with a small hammer till it is cool enough to hold
Grind it off if necessary - done
Brazing won't be any good well not if you drive it nice and hard anyway as the manifold will get hot enough for the brazing to melt out -- tried that
Willy
William Revit

Another oprion is to drill the hole round and drive in a steel plug. No welding or heating. Of course you need access to the inside to cut it flush.
Art Pearse

My solution would be to drill and tap the hole and fill with a short bolt that does not protrude very far into the interior.
Frank Grimaldi

Weld cast all the time with a wire welder and mild steel wire w/CO2 gas back. Length of the bead depends on the crack. Shorter beads work best and pecking the weld with a chipping hammer during the cooling process somehow deters cracking.
T Lea

I agree with Frank Grimaldi, for the best DIY solution just drill out and tap (don't full tap all the way through) and then fit a bolt which will tighten and finish short. Careful!!!! don't tighten too much - you might crack the casting. If appearance is important, cut the bolt off and grind smooth.

Jeff - let us know what you did to sort out this problem.
Brian Shaw

This thread was discussed between 13/11/2011 and 21/11/2011

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