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Can cracked exhaust manifold usually be repaired with welding?


tdskip

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Good morning and happy Friday.  This is the exhaust manifold for my 1974 Tii, and as you can see there's a crack in it. 

 

I am decent with a MIG welder, and was thinking about sandblasting and then trying to weld the crack closed but I'm not sure if that's a fools errand.

 

Is that sort of repair are usually successful in long-lived, or is it time to find another manifold? 

 

OR,  do I take this manifold away in the garage somewhere and find a header? 

 

What do you think gentlemen?

 

 

IMG_5176.JPG

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It’s definitely do-able but whether a MIG with mild steel wire is right is a different question. Not familiar with welding cast iron but an arc welder with the right rods might be right. MIG welders can chime in here with what the correct wire would be. 

rtheriaque wrote:

Carbs: They're necessary and barely controlled fuel leaks that sometimes match the air passing through them.

My build blog:http://www.bmw2002faq.com/blog/163-simeons-blog/

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I think I would start shopping.  Hopefully someone will chime in and say "all you've got to do is ____", but that part has a hard life and I can't imagine a weld lasting long under those conditions.  My guess is the next crack would be right alongside the weld.  I might be tempted to tig it up, just for the 'sport of it', but I'd be keeping my eye open for the replacement.

 

sorry for the pessimistic response,

Tom

 

PS, I bought a tii manifold once that had a crack between three and four.  I sent it back, even though the crack was much smaller than this one.

 

     

 

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The problem with welding the cast iron manifolds (any of them) is the weld is only going to penetrate less then half the depth of the crack.  Its like placing a band aid on a stab wound, it might stop the bleeding for a minute, but it will quickly start bleeding (or leaking exhaust gas) somewhere else.  Basically its a temporary fix with an unknown length if time before it cracks again.  Stubby header time?  

.02 for what that's worth.

Matt

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It can be welded successfully, but probably not by you with a MIG welder...What you need is a shop that specializes in welding up cracked engine blocks, which typically are cast iron.  Some machine shops do this, but not all.  

 

I would do a search for a "cracked block" service.  A machine shop or large garage that specializes in heavy truck or marine engine repairs are gonna be your best bet, as typically those engines are worth the trouble of repairing a cracked or damaged engine block.  And if you're in a large city or one with a lot of manufacturing, look for a company that does machinery repair/rebuilding.  They'll have the equipment and expertise to heat and weld cast iron.  

 

I watched a welder successfully repair a cracked six foot diameter, cast iron gear wheel--with a crack from the hub to the rim on one spoke, then build up the teeth with weld so they could be re-cut.  It was from a punch press originally built in 1865 and steam powered.  And still in use!  Repairing a manifold at such a shop would be a snap.

 

Good luck

mike 

Edited by mike
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'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
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The tii manifolds are supposed to flow better than the standard manifolds, so are considered an 'upgrade'.

There is plenty of reading on that topic in the archives, if you are interested/curious.

 

One thing that is key to welding cast iron is that you have to preheat the whole piece and then cool it slowly and evenly.  

     

 

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If you have an oxy-acetalene setup, and understand how to pre-heat and maintain during the working time, you can braze a manifold quite successfully.  Check these guys out.

 

Cast Iron Welding Specialists Lock-n-Stitch

 

As you can see from the site above, welding cast iron is usually reserved for really hard to replace parts, that cost a whole bunch of money.  Although a manifold is small and would be easier to pre-heat and keep hot during welding.  The link below gets you to the Muggy weld site.  They sell a brazing rod that is supposed to be great for cast iron.

 

Muggy Weld Cast Iron and SS Soldering Rods

 

Jose

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I have successfully fixed BMW cracked exhaust manifolds in the past with great results. I did one for a friend of mine almost 6 years ago on his tii and is still OK   I braze them, not weld them. Have to heat cast iron up to cherry red before brazing and then a very slow cool off period   Worth a try, what else are you going to do with the manifold?

 

 

Thanks, Rick

 

 

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16 minutes ago, stephers said:

what else are you going to do with the manifold?

If unsuccessful, there's always the neighbor's pool...

'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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They CAN be preheated and welded with a stick welder and nickel rod,

as well as brazed.

 

The limitation is physical- if you can't access the entire crack,

through all surfaces, welding or brazing probably won't be a long- term

solution.

 

But if you can drill both ends, fillet it to about 50%, and then lay in a

good bead of nickel alloy rod, it will last for decades.

 

If you fix the lean condition that cracked it in first place, of course.

 

 

Oh, the mig won't work, btw- the transition zone will be brittle and separate

as you weld. It feels like 'it's just not sticking'

 

btdt,

t

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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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+1 with the preheat/brazing team. Forget welding with steel...it will immediately crack right next to the weld and the metal's full of carbon. We would grind out the crack to a deep V, going beyond the ends of the crack, preheat in an old oven to 400*, braze up quickly with a soft rod and immediately bury in cat litter or sand until cool. Done a bunch, lose about 1 out of 10.

 

 

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