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.
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.
It is retained with a through bolt, so no turning, only hammering.
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.
Heating may take some of the hardness out of the boss.
Only way heat will shrink it is with welding rod in the heat.
Never say never. I've seen some old timers who knew a bit about metallurgy do things that many said could never be done.
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 .
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.
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.
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
What is a split bolt?
Not sure, but here is a picture to end any possible confusion.
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.
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.
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.
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.
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.
I might add that I screwed myself out of quite a cash flow doing that. But did make some points!
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.
The collar is to keep the pin from turning in the boss. It usually doesn’t touch the OD of the pin. Heating the boss will make the steel expand making the hole in the center get bigger, not smaller. The steel used for the house frame has been mild steel in all my experiences. I’ve never seen bushings work in a boom foot. They usually crack and break in pieces when someone starts to impact load the boom.
The general rule of thumb is to have as much support at the bosses to equal the diameter of the pin. So if you have a 3" pin you should have 3" of support for it at each end. "From a machinists point of view" The lovely engineers always try to cheat that a bit. They are keeping tracked of cost. Those two machines the way I did them the boss when cooled shrunk onto the pins. However you are correct that boss with the bolt its only purpose is to keep the pin from spinning.
fingers crossed. I have a couple of pairs of bushings waiting for this to come apart. I'd tear into it now, but I *might* need it on the next job, a really muddy mess where it might be handy to reach bedding in to the mini.
I know how that goes. You can't always fix it at the most optimum time. Everybody has to have a hamburger.
I confirmed with a second manager at a different Pape equipment facility on the heating thing. He said it was good for a maximum of .020~.025 No quenching, not a ton of heat. We'll see if I even get to try it, when the new pin comes in.
Just did some stick, bucket pin and bush work on a 490D a couple of weeks ago for a fella and we measured .068" vertically between the boom and house... since it is a low use machine, we will measure it again in a year or so and see what the indicator reads. If it is significantly worse, we will weld, bore, repin and bush then. Regards, Bob
Also, meant to add above that I agree with most said regarding the pin bosses and such... not so sure a .020-.025 bore reduction is achievable regardless of technique/method by heating. Regards, Bob
I think by split bolt big rich meant some sort of expanding pin https://www.nord-lock.com/expander-system/for-any-machine/ There are many brands but I have no experience with them maybe someone else has seems like a plausible solution to keep that bore from getting pounded out again
I'll set up some tooling to measure it if i try it.
yea that's the bolt i used one at work seems to be doing good
Heating will work, if done properly. To put a fine point on it, you are using heat to cause localized upsetting. Its a similar process to welding distortion. What happens is you heat a small section of metal. The metal wants to expand, but it can't because it is restrained by the cold metal surrounding it. But the forces of expansion are stronger than the strength of the metal, so the metal compresses itself. Now when the metal cools, it pulls the surrounding metal in, making the bore smaller or a beam bend. Lincoln Welding has many old videos on Utube. One on welding distortion illustrated this by putting a steel bar endwise in a vise. Tighten the vise so it holds the bar. Now heat the bar in the middle. When the bar cools, it will fall out of the vise. If you wish to know more about the subject, look up flame straightening.
I have done a fair bit of repair on bores like that over the years. As said above theres no fix like building up and boring .Machine frames are generally mild steel/50000yield material so they accept buildup well . Pin bosses like that are always out of round once you measure them properly. In my days of line boring we always built up by hand . Now days with a bore welder its pretty quick with the right guy on it. If your going with a new pin id be line boring while its apart. We made a lot of pins ,mainly stick to bucket when built thumbs as OEM didnt supply long enough pins. 4340HTSR and then induction hardened always worked well. Always used OEM bushings wherever possible , or Torrington bearing races where we couldnt size a bushing. Any shrink fix you might accomplish will work loose pretty quick and maybe be worse.