cast iron exhaust manifold repair

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We have a 1964 snow blower that has a Wakasha 140g 6cyl. engine, ithas a two pice exhaust manifold that has been welded by me ten years ago and that weld is holding well now it has cracks on the inside curves of the runners. need some advice as to build a new one or try to fix it. I'm concerned to the fact it will shrink and not bolt back up to the heads. just the rear section of this manifold is $3000.delivered to our shop and the other half is not to be found. here are some pic of the unitLife is tuff,so be sharp  lincoln sp 100  cutmaster101  miller bobcat  miller 250 mig  $thousands in snapon
Reply:Hmmm, preheat and braze it or PREHEAT and weld it with some high-nickel filler?  The best laid schemes ... Gang oft agley ...
Reply:Yes I know how to do it but at this point is it worth it,if it were completely broken it would be no problem but if I try to do anything at this point will I be causing more problems. i cant pre and post heat with it on the engine.  I used a nickel filler on the other weld but it was broken apart.Life is tuff,so be sharp  lincoln sp 100  cutmaster101  miller bobcat  miller 250 mig  $thousands in snapon
Reply:A big benefit of preheating is reducing or minimizing thermal coefficient of expansion (and contraction  ) problems.If you can get into the engine bay to braze, you probably have a ready-to-go way to preheat the part for brazing.  Just run the engine until things are warmed up!  Only 'gotcha' there is if the crack is clean enough inside for the braze and flux to work properly.  And for the crack width to be the right size for the brazing filler to flow into it (not too wide).If the manifold is unobtanium, then your choices are to fix or make.  Fixing is -usually- easier than completely making parts.If you can't preheat the manifold (sections) hot enough for welding, then that pretty much limits that option.  I'd be leary of trying to weld some 'critical' dimension parts in the 'cold mode', to much problem of thermal contraction and dimensional change IMHO.If you can't braze or weld it or buy it, then that means you have to fab it.  Headers, anyone?  Maybe castweld/Peter will chime in with some advise.  The best laid schemes ... Gang oft agley ...
Reply:why cant you pre and post heatby running the engine may be better than nothing
Reply:I can't tell by looking at it but if the exhaust manifold is separate from from the intake runner you could always make a header for it out of flanges and tubing.  there's a lot of stuff out there for people who do engine swaps and need to make custom exhausts to make everything fit.
Reply:Most small manifold cracks are superficial or quickly carbon over and don't leak.Unlike this one:  Attachment 41518If there's a leak or noise issue it's probably from the packing between the manifolds, or the mounting gasket,  not the hairline fractures.To pinpoint exactly where the exhaust leaks, feed some diesel fuel into the carburetor while the engine is warm and running, see where the smoke escapes.Good LuckLast edited by denrep; 10-19-2010 at 11:43 PM.
Reply:I am just learning about repairing cast so I can't help you as far as comparing dificulty or time and money between repair or build new but it does look like it would be a very quick and easy piece to make. I would find someone with a waterjet or flamejet or something to make your flanges. If you have a gasket they should be able to cut a shape straight off that. Otherwise I think a pic with dimensions or a tracing or something would probably work too. Or maybe just taking the mani in. Since it's pretty industrial lookin and strength and longevity look more important than weight I'd find thick wall exhaust tubing and then weld it all up.You could get a little fancier with the routing just to try to get everything flowing a little smoother but if you just went with the basic log style like that I'm sure it would be fine for the application.Or you could go all out with equal length header and a proper collecter Try to get tubing close to the ID of the mani. If anything a little larger but not much. It try and stay as close as possible but err on the larger side.
Reply:Why not just build up a log header and get it plated? Jet-hot, nitro plating, etc. You'd be surprised at how many pre-fabbed flanges are available to get you started
Reply:I don't have much to add on the issue of welding up the manifold, but you might want to increase the fuel jet size in the carburetor a step or two.  The manifold might be getting too hot due to a "lean" fuel conditon.  Slightly more fuel might help prevent this happening in the future.Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:I can see the problem continuing.  I vote to do a fast fix then make a log.  Fire up the engine to preheat, use ni-rod to weld over the cracks and peen the welds.  After the repair fire up again then let cool.  Buy new gaskets and make a set of steel flanges at least 3/8 thick.  For the steel tube use heavy wall at least 3/16 thick.  Steel does not last at high temp but if heavy wall should last many seasons.  When building your log manifold tack everything together on the engine.  Remove it and tack weld the flanges to a very heavy plate or some other flat material at least half inch thick.  Weld the assembly up and let cool before grinding the tacks and breaking free.  Rectangular tubing is easier and you are not making a race car.
Reply:It was molded 10 years ago? Really a long time. I was still a kid ten years ago. Any way. You can just remold it so it can still last. But I don't think that it will last much longer in that condition.Exhaust Manifold
Reply:I'd say remake it in schedule 40 SS weld el's & pipe, should last forever. wouldn't be too hard to even make the flanges with a plasma cutter...of course you could also turbo charge it too while your at itmiller 330a bp TIGmiller dynasty 200DX TIGmillermatic 185 MIGthermal dynamics cutmaster 101 plasma cuttersnap-on YA5550 plasma cutterhypertherm powermax 30 plasma cutterbaileigh CS225 cold sawetc....