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  1. #1
    retro jet's Avatar
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    welding crank case reccomendations?

    I have two 951 cases that are cracked. The cracks just below the cylinder don't appear to go thru and seem like easy welds. But one is cracked into the balance shaft chamber and the case sealing surface looks slightly distorted (low). I figure I will "v" notch and weld. Grind any bead above the case seam and fill any distortion with JB Weld. This sound like a good approach?

    Anybody got welding reccomendations? What alloy is the case or what filler rod to use?
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    Last edited by retro jet; 06-11-2010 at 10:15 AM. Reason: added pics


  2. #2
    I have done several cases with good results. That said, this is not a job for a novice welder; how good are your aluminum TIG welding skills? You need to be an above average aluminum TIG welder to expect any success at all. (I've got a Miller Syncrowave 350 that is a real workhorse...I wish I had one of the newer inverters like the Dynasty 350)

    The general rule is the case cannot be cracked into the case sealing surface. However, yours doesn't seem too bad; I might be tempted to try that one. You really need to be a pro to tackle that one....

    4043 rod works great on these cases, and I use a pretty sharp profile on a 2% lanthanated tungsten. (don't bother trying it if you are an old school balled-pure tungsten welder...) The main problem with cracks is cleanliness. That crack will have oil in it, and when you weld it, the oil will come out and ruin the weld. You need to get the oil out first.

    To start, the whole case must be cleaned, and cleaned good; no trace of oils anywhere on the case surfaces.

    The cases must be bolted together and torqued to spec to prevent warpage. (that is a main reason why welding cracks that extend into the parting halves shouldn't be fixed...) I would use solvent to soak into the crack first (acetone) then "wash" over the crack with the TIG torch to expel the oils, cool, clean again, wash with torch, over and over. Then use an aluminum oxide burr to open up the crack some, followed by TIG torch wash. Finally scrubbed with a clean stainless brush on both sides. Then you can weld.

    To get around the oil-soaking-into-crack problem (thats what SHE said!) I have cut out the area and cut a matching patch from a donor case to weld in. That way, the cut area doesn't suffer from the oil problem, and is actually quicker than just trying to seal up a crack.

    The actual welding takes like 2 minutes, vs an hour or more cleaning and prepping.

    Regardless, you may end up with some porosity. To be safe, I grind it down and coat with a layer of epoxy, then paint to make sure it is sealed. Looks better that way too.

    I've got a '01 XPL with a hole in the case waiting to be fixed......

  3. #3
    SURFnTURF's Avatar
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    I wouldn't worry too much this set was repaired and rebuilt 3 years ago and still going strong.
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  4. #4
    carnage Trevor!

  5. #5
    retro jet's Avatar
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    Dood, that is the best case welding info I have found here. Thanks man.

    My welding skills are terrible, so I appreciate good welding that much more. I am going to bring this to a precision sheetmetal shop. I challenge these guys with welding thin gauge aluminum (5052 & 6061) all the time. I hope their skill in not melting away .02" and keeping it flat will carry over to this. I am not sure what their rig is though.

    I was wondering about whether I should bolt the cases up to help keep them straight, but forgot to ask and kind of talked myself out of it. That is good advice.

    I was going to notch with a tungsten carbide burr in a dremel, is there a reason you specified a Aluminum oxide?

    About the crack in the sealing surface... We can fixture the case to hold it flat. They use copper sheet or bar stock to draw away heat from long seams on complicated sheetmetal. So maybe we can clamp some copper bar stock either side of the crack. This case has a lot more mass than most of what they are used welding, so If the welder thinks he can do it, I'll go for it.

    The visible length of the crack is about 5/16". Anybody think I should just fill it with JBWeld? Id like to at least tack weld the top.

    Pressure Test!!

    BTW, that is some impressive case damage. I had the piston skirt and bottom of the cylinder sleeves break off and this is all that happened to the case.

  6. #6
    SURFnTURF's Avatar
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    You can weld cases anywhere except on the machined bearing surfaces,you can even mismatch them and have them line bored for crank run out all depends on how much time you have or hands on skills with precision machines.Those are very minor cracks.

  7. #7

    Smile

    CLEAN,CLEAN CLEAN.THen Have a proffesional welder who is very proficent at welding cast aluminum do it.OR if you have to do it yourself I have patched exhaust manifolds and cases, with an alloy brazing rod,they make some special alloys that melt at about 500 degree less than aluminum,however you heat the aluminum up enough to open up the pores ,brush with clean stainless steel brush,then make a tinning pass with a light coat, scrub again with stainless brush then proceed to fill it.Trick to getting it right is clean,stainless brush,patience,hope this helps oh I use a rod called HTS2000,lots of old timers scoff at them,but they work>Marvin

  8. #8
    retro jet's Avatar
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    results

    Here are the results of welding done by a precision sheetmetal shop. BTW, they typically use 5356 filler for welding 5052 alloy, so if you decide to go to a sheetmetal shop, talk to them about using 4043 filler. After sea dood reccomended it, I poked around some welding forums and it seems to be used for the widest range of aluminum alloys. The welder was worried about the cast cases being porous, but had no problems and said they were high quality.

    I had the welder build up a bead on the edge of the intake that had broken off and filed and ground it back to shape. I traced the good MAG intake and matched it.

    He also welded a broken intake grate.

    I cleaned the cracks with acetone, a wire brush, and compressed air, multiple times. Then heated with a heat gun to draw any deep oil out. and repeated.
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    Last edited by retro jet; 06-11-2010 at 12:10 PM. Reason: added "cleaning"

  9. #9
    retro jet's Avatar
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    filled with JB Weld and sanded flat

    I glued 180 grit sandpaper to the center of a parallel (a precisely ground flat and parallel bar) and sanded the mating surface that was welded. When the bead was taken down, the immediate edge was still .004" low either side. Loctite 518 can fill .005" gap, but I liked filling it with JB Weld better. I also painted around the external weld bead with JB thinned with acetone to make a fillet as added protection against an airleak from porousity at the weld. I am not planning on grinding the external weld. Needs paint.
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  10. #10
    Nice to see you made out well with your case repair. Good point about the filler. 5356 is a great filler for structural work, but not good for case repair. It is very brittle and cracks easily. Plain old 4043 works best.

    BTW, DON'T use Loctite 518 for sealing cases! It is an anaerobic compound that often doesnt set up properly, and ends up brittle and can crack and leak over time. It took BRP many years to figure it out. (they didn't switch over until 2001....) I think there are many good 787 cranks being replaced now, because of apparent leaky inner seals, when in reality it is the cases leaking because of loctite 518 failure.

    Use a good quality silicone-based sealant like Threebond 1211, (or Yamabond, Hondabond, etc)
    Last edited by Sea Dood; 06-14-2010 at 05:43 PM.

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