repair crack on cast iron piece on heat exchanger

Discussion in 'Diesel Engines' started by xaliba, Jun 16, 2018.

  1. xaliba
    Joined: Jun 2018
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    xaliba Junior Member

    Hi folks,

    there was a tiny little drip coming out a cast iron piece on the heat exchanger as the engine ran. Opened up and it appears there's a crack there and not just a faulty seal, the piece is quite old and not sure it could be welded without further damage. It's the cover which directs raw water from pump into the rods which exchange heat with fresh water. Thought of covering the whole piece on the inside with sikaflex until I can find a replacement, any thoughts?

    thanks
     

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  2. philSweet
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    philSweet Senior Member

    Sika flex isn't rated for that temp, it would be marginal at best, and having to rod that stuff out of your exchanger tubes will certainly make you wish you hadn't. JB weld, done properly, can fix this until something else gives way. And locate and replace the pencil zinc in the other end of the exchanger.
     
  3. xaliba
    Joined: Jun 2018
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    xaliba Junior Member

    Hi Phil,
    thanks for commenting.

    I thought of sika because unless there is some problem in the heating system this piece does not get hot at all since it has seawater coming straight into it from the pump. Zinc is under control. Have you had problems rodding the silt out before?
     
  4. philSweet
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    philSweet Senior Member

    From memory, Sika is good to about 66C, 3M4200 is good to 88C, more if you don't really care about strength. But turbulent water flow and temperature cycling are going to challenge any bond. Can you at least blast it bright clean and die-grind the crack?
    Loctite superglue is rated to 82C, it is lowish viscosity and might to better than a smear of sealent, but I haven't tried it on a pinhole or crack in iron.

    The elbow on the piece is the exit for the raw water, correct? If so, it could get fairly warm since half of it is exposed to warm seawater. And it could get really warm if you leave the seacock closed until the the engine boils it's fuel.
     
  5. xaliba
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    xaliba Junior Member

    I don't understand what die-grind the crack means.

    one pipe is where the water gets into the rods, the other is the exit as it comes out the rods, it could get lukewarm in normal conditions at the very most, but yes, if the engine overheats it could get quite warm.

    You mean the regular superglue which dries out in a few seconds which normally comes in a tiny sort of metal tube?
     
  6. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Die-grinders are very small grinders. Usually;
    - Pneumatic
    - 1-3 inch grinding wheels
    - 1/4inch collets hold various cutting or grinding heads
    So larger than "Dremmel"

    Use to smooth and clean surface

    Locktight is a brand of superglue, it is thicker than most cyano-acrylic (super) glue.

    If my boat, I would
    1 replace part
    2 ask local welder
    3 high-temperature epoxy
    4 superglue

    Be prepared to collect any surface coating from down stream

    Good luck
     
    Last edited: Jun 16, 2018
  7. Angélique
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    Angélique aka Angel (only by name)

    It looks like weldable to me by a specialist like in the below cast aluminum example, it isn't oil soaked till deep in all pores which would make it worse, water and air parts give the least problems with welding, maybe best shot blast it first, then I suggest to follow the same procedure as in the below video, use the detection sprays to find all cracks and their ends, the crack ends need to be drilled to prevent further cracking by welding stress, and also inspect the other side if it's there the end too, then grind the cracks into a V first, it may be needed to machine the piece after the welding to flatten the sealing surface, and to restore the blind hole in the middle if needed, but best first talk to the person who's gonna do the welding, the latter off course only if the welding isn't a DIY job...


    Good luck !
     
    Last edited: Jun 17, 2018
  8. Angélique
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    Angélique aka Angel (only by name)

    Last edited: Jun 16, 2018
  9. Angélique
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    Angélique aka Angel (only by name)



     
  10. Angélique
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    Angélique aka Angel (only by name)

     
    Last edited: Jun 17, 2018
  11. Angélique
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    Angélique aka Angel (only by name)

    It's already well explained by Blueknarr, but I'll guess a link won't hurt: Die grinder
     
    Last edited: Jun 17, 2018
  12. gonzo
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    gonzo Senior Member

    You should be able to get it welded. Silver bronze alloy is the best, but regular bronze can do OK. Locally, that is: soldar al acetileno con bronce. It is better to heat the whole piece first.
     
  13. Lepke
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    Lepke Junior Member

  14. Angélique
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    Angélique aka Angel (only by name)

    That would be brazing and not welding, it can be done with an acetylene+oxygen torch and flux, and according to Lepke's post #13 specialists link it would be much better than electric welding for cast iron, it says¹ preheating of the whole piece before brazing needs to be at least 900° F (482° C) and preheating needs to be done slowly, the same goes for the cooling down.

    ¹ See also at the bottom of that page the PDF Understanding cast iron and repairing damaged castings permanently.
     
    Last edited: Jun 17, 2018

  15. Angélique
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    Angélique aka Angel (only by name)

    Here's some pretty basic links about: Brazing -- Flux -- What is Torch Brazing ?



    P.S. - The video looks OK, except that it looks like he didn't preheat the whole piece.
     
    Last edited: Jun 17, 2018
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