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welding cat 426 backhoe boom

Discussion in 'Tractor/Loader/Backhoes' started by gusbratz, Dec 14, 2012.

  1. gusbratz

    gusbratz Well-Known Member

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    This 1990 426 cat I picked up only has 2200 hours on it but the backhoe is all beat up for some reason. Not sure what they were doing to it or if it is just because armatures were running it but it has had some previous repairs and currently has a small crack in the bottom cast section of the boom. I have welded plenty of cracks up in my 1960 case with a fabricated boom but this boom has a cast section at the bottom where the main pin goes through the bottom and has a small crack in one of the oval holes where the hydraulic lines are accessed. Is this what they call ductile iron? Can I weld it the same as my old fabricated one? I normally would 1.)Clean it off 2.) V it out 3.) Root pass with 6010 4.) Cover passes with 7018
    I will try to post a pic but I can’t figure out how to get them to be the right size and to forum won’t let them post.
     
  2. surfer-joe

    surfer-joe Senior Member

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    It's cast steel, Gus. It does not take well to crack repair by any method. Been there! Done that! However, you should check with a Car dealer service department for some technical advice. Maybe they have a new trick that I'm not aware of. Best fix I know of, is a new casting, or maybe you can find a good used one, perhaps off a burned machine or one that has been wrecked. Check on the internet for availability, and maybe give Foley Tractor or Beckwith a call to their used parts divisions.

    Good Luck!
     
    Last edited: Dec 14, 2012
  3. RayF

    RayF Senior Member

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    If the casting is welded in it will be weldable.I would do it pretty well as you describe. Vee it out and put in a backing plate if possible and use a good pre heat and 7018.
     
  4. SchuLace

    SchuLace Well-Known Member

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    If you choose to go used, check out T&E out of Montana. We have had good luck with them.
     
  5. norite

    norite Senior Member

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    If it is weldable, ditch the 6010 for the root, weld it all with 7018, might want to go to a higher tensile strength rod (8018, ...11018) depending on what grade of steel it was made from. Also preheat and postheat may be necessary, your cat dealer should be able to tell you if it is weldable and if so, what the welding procedure should be.
     
  6. mitch504

    mitch504 Senior Member

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    Yeah, like RayF said, if it is welded to the rest of the boom, it is obviously weldable.
     
  7. gusbratz

    gusbratz Well-Known Member

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  8. gusbratz

    gusbratz Well-Known Member

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    little crack in the useless hole in the lower boom casting
     

    Attached Files:

  9. gusbratz

    gusbratz Well-Known Member

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    it takes waaaaaay longer to resize, save, link, upload and post pictures than it does to weld up cracks. good thing im at work...........any way the PO didn't do these said they were welded like this when he got it.
    lwer castin craxck.jpg patch on main boom pin.jpg porly done.jpg right hand crack.jpg
     
  10. Lee-online

    Lee-online Senior Member

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    There was an old update to fix cracks and add reinforcement plates where the boom cylinders mount to the boom.

    I'll see if i can find it.
     
  11. Mike.580ck

    Mike.580ck Well-Known Member

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    I do a lot of Silver soldering in my small business , i silver on the diamond and carbide cutters on oilfield bits that go thousands of feet in the ground and it holds up, What about silver soldering the smaller cracks it gets pricey but the stuff is tough any input on that idea ?
     
  12. Oxbow

    Oxbow Senior Member

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    Tom V has a post on this forum entitled "some work picture", judging from the pictures on his thread I would definetly respect his opinion. You might go on that thread and ask him.
     
  13. Nige

    Nige Senior Member

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    IMHO that backhoe boom has been welded by a complete and utter amateur ......!! Sometimes you just have to bite the bullet and tear stuff apart to weld it rather than trying to "butter over the cracks", all it does is come back and bite you even harder further down the road. Really what that boom needs is complete disassembly, steam clean, then remove all the paint and let's see how it looks. From the photos I personally think it's salvageable but sometimes that's not the same as seeing it in real life.

    I'm not at work for the next 3 weeks so accessing technical information's a bit difficult. However it might pay you to post here the 3-letter prefix for your machine here just to help Lee find the relevant procedure for updating the boom as he mentions above.

    For information of everyone. Any fabricated Cat structure, whether it contains castings or not, is designed with the capability of being weld-repaired using E7018 electrodes or a similar specification of all-position welding wire. There's no need to go into roots with 6010 as some people think, go for it with 7018 right from the start. however as my old grandafther always used to say the job is "99% preparation and 1% perspiration", sometimes you really have to carve into the structure to create the necessary access to weld the crack, even to the extent of cutting a window in the structure and then welding it back in afterwards. Not doing the correct preparation before repair welding is the most common error I've seen in the past. Sometimes castings that are part of fabricated structures might have a slightly different weld procedure for a crack within the casting itself but as regards the weld between the casting and the structure the same procedure applies as with structures.
     
  14. Scrub Puller

    Scrub Puller Senior Member

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    Yair . . . well I dunno.

    Unless it's my eyes the only possibly active crack I can see is the one through the hole. Bad and all as they are the other welds and patches seem to be holding which shows the thing is not much problem to weld.

    If you are worried about that little crack vee it out and weld it otherwise just centre dot and watch it.

    Cheers.
     
  15. gusbratz

    gusbratz Well-Known Member

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    thanks for the replies guys. I would like to see that cat boom reipar bullition. machine is a 7BC00502. can you tell what year it is from that? I am not sure what to do about this boom, Like scrub said the patches are ugaly but they are holding so if it ain't broke don't fix it....but i am pulling all the hyd, cyl's to repack them and with all the cyls off it would be a good time to air arc those patches out and lay some better weld onto them. or at least see whats under them.
     
  16. norite

    norite Senior Member

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    Since this hoe is "new to you", and you say you are removing and repacking all the cylinders anyway, it would take only a little more work to remove the boom and re-do any of the patches that were previously poorly done. You would also get a chance to make sure the underlying cracks are not growing underneath the patch plates. At least that is what I would want to do, but I am a welder and have equipment to do this. If you can do the welding properly yourself that is probably what you might consider doing.

    You might want to look for a clean used replacement boom if you can find one at a reasonable price, a lot of people when they see non oem welding on a machine either devalue the machine or perhaps won't consider buying it. If you don't intend to sell or trade it in the near future, this is not a big deal.

    Good luck, send some progress pics and make sure to let us all know how it all turns out.
     
  17. gusbratz

    gusbratz Well-Known Member

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    Made some progress today, figured I would get some work done before it snows and while I still have my old backhoe to do the lifting with. I pulled all the lines and the boom and dipper cylinders. Then I pulled the dipper and attempted to pull the boom. It won’t come off with the pin removed.. Do I need to press those bushing out? They maybe migrated over a little and are working like pins?
     

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  18. Scrub Puller

    Scrub Puller Senior Member

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    Yair . . . gusbratzThat could well be the problem mate, the bushes could have moved . . . one thing I'll mention, when I take rams off I always like to get the rods pushed up inside straight away.

    If you leave them too long like in the picture some thing always seems to get dropped and chips/bruises the chrome or they get some weld spatter . . . just sayin'

    Cheers.
     
  19. gusbratz

    gusbratz Well-Known Member

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    cat426backhoelines004_zpsd0069a4c.jpg got the boom off and into the garage and now i need to decide how to make this patch right.
    cat426backhoelines003_zps64b0a2a6.jpg
     
  20. bae216

    bae216 Member

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    I have welded up front weights on a tractor that were cast material. I used nichol rods and took the flux of the rods then heliarc them with a tig welder and it worked great. I would say go with nichol rods either way if you wanted to stick weld or heliaec, it just don't look as good with the stick welding. Preheat is a must.