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Shrinking bores with heat

Discussion in 'Shop Talk' started by skyking1, Nov 28, 2020.

  1. skyking1

    skyking1 Senior Member

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    I am rebuilding the company JD120 excavator, and the shop foreman at the dealer suggested some heat to try and shrink the big pin boss on the main frame. I will check it when i have the boom off and new pin in hand. It may only be a few extra thousands oversized, and he said they had some success with that.
    Unfortunately he did not elaborate.
    I have been thinking of strategies for it. One that came to mind is some moderate rosebud torch heating for a good long while, then a couple of strategic weld beads on the boss. Let the welds pull it in a bit with any luck and planning.
    I won't expect miracles but I also don't just toss money at things either. If it is not too bad I can live with a little play, as long as the pin and bushings and most importantly, the boom bores are good. I will get line boring as needed.
     
  2. GaryHoff

    GaryHoff Senior Member

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    If the boom pin was turning in the boss, then the boss likely wont be very round. Good luck shrinking it down, your plan seems like it could work if the boss isn't worn too badly. Post some pictures, would be interesting to see how this turns out.
     
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  3. skyking1

    skyking1 Senior Member

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    It is retained with a through bolt, so no turning, only hammering.
     
  4. John C.

    John C. Senior Member

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    Heat will make it expand and get loose. Hot then cold can make them contract to a different dimension but it isn't something I would try. All I've ever had luck with is weld up and bore to spec.
     
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  5. Bls repair

    Bls repair Senior Member

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    Heating may take some of the hardness out of the boss.
     
  6. DMiller

    DMiller Senior Member

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    Only way heat will shrink it is with welding rod in the heat.
     
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  7. excavator

    excavator Senior Member

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    Never say never. I've seen some old timers who knew a bit about metallurgy do things that many said could never be done.
     
  8. Volvomad

    Volvomad Senior Member

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    I wouldnt have expected the steel plate the pin bosses are bored in would be hardened .
    If the boss was heated rapidly all around the inner edge to red ,guessing maybe to 1/3 of the way out towards the edge of the plate ,as the other 2/3's of the boss would be much cooler ,would any expansion be forced inwards ? Let it cool ,measure and maybe repeat . Never heard of any of this before, just thinking aloud .
     
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  9. Theweldor

    Theweldor Senior Member

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    It could be done. However a rosebud would not of be the tool of choice. A large blowpipe would work much better. It would only be a temporary fix I would think. The bore would be no where near as true as line boring. I have 2 line boring steups and have flame straightened 80 ft long 48" tall beams over the years. The bosses being built up sections would take some patience.
    My opinion is you wouldn't save any money and you would have a much better job line boring the bosses.
    Just my 2 cents.
     
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  10. lantraxco

    lantraxco Senior Member

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    Any time you heat steel to red or beyond, it will shrink some when it cools. My old man was a foddy and bender (sic) guy back when cars and trucks actually had some metal to them and bondo was a distant dream. He could pound out most dents and with a torch and a cold wet rag shrink most of the stretch out of a body panel. Then lead to finish if required. In my experience the plates and bosses that hold pins are not at all heat treated, so I wouldn't worry too much about that, but I've never been able to get more than a couple thou shrinkage on anything I tried it on. Weld and bore, or bore and sleeve, or make an oversize pin all work.
     
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  11. bigrich954rr

    bigrich954rr Well-Known Member

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    Get a rose bud torch heat it from 11 o’clock to 12 o’clock in a strip Not just a round spot . Then heat it at 6 then 3 then 9 then check it then heat the spots like 2/4/8/10 check again .

    The end should not be heat treat as it’s welded on the end of the shaft .

    they also make a split bolt that takes up the slack
     
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  12. Volvomad

    Volvomad Senior Member

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    What is a split bolt?
     
  13. skyking1

    skyking1 Senior Member

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    Not sure, but here is a picture to end any possible confusion.
    IMG_20201129_145910.jpg
     
  14. DMiller

    DMiller Senior Member

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    Soft steel, easier to weld and line bore as will not stop stretching. Best bet over bore and Bush it out. That is a Pinch Bolt in most cases, a Lock Bolt in this instance.
     
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  15. Theweldor

    Theweldor Senior Member

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    You can do as you wish. I have not a penny invested but that needs welded up and line bored. There is quite a ridge at the top of that bore.
     
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  16. skyking1

    skyking1 Senior Member

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    I'll get the new pin in hand and check it out and report back. Hopefully as soon as next week.
    The plan is to unpin and secure the boom so I can check out the bushing bores, and check the house there with a new pin. If i can install new bushings in the boom without line boring, i will do that. There's just no way to know until i get it apart.
    Same goes for those house bores. If needed they will get line bored, as well as the lower cylinder pin bores.
     
    Last edited: Nov 30, 2020
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  17. DB2

    DB2 Senior Member

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    The boss on the house looks like nothing more than a collar welded on the structure. Doesn’t seem like much support for such a large pin.
    Need to see a picture after the boom is removed to know for certain.
     
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  18. Theweldor

    Theweldor Senior Member

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    I do line boring for a company here. They have a 345 and a 365 that only run hammers. It used to be a yearly thing to bore them. The general rule of thumb is to allow .001 clearance for every 1" diameter of the pin. I got tired of doing them every year so the last time about 4 years ago I allowed .001 clearance for the pin. In order to install the pins when I bored them last you had to warm the bosses to I think it was 450 degrees above ambient temperature to get them to fit. The formula is .00000633 per degree per every 1" in diameter. They have lasted for 4 years at the moment and as far as I know they are still tight. You have to have your ducks in a row when you put them back together as you only have so much time before things can go awry. Most of the material that stuff is built out of is not exotic but it is in 572 gr 50 or better range. You don't want to be heating it up red hot to repair it.
    Just my 2 cents.
     
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  19. Theweldor

    Theweldor Senior Member

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    I might add that I screwed myself out of quite a cash flow doing that. But did make some points!
     
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  20. skyking1

    skyking1 Senior Member

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    I think most of the machine's wear is due to extensive hoe pack usage. If I end up line boring the house, I will request that they fit it tight as you specified above. It can't hurt for sure.
    Red hot was never going to happen, LOL.
     
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