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Komatsu PC75UU2 offset boom to std one piece boom

Discussion in 'Excavators' started by Batkom, Jan 31, 2019.

  1. Batkom

    Batkom Well-Known Member

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    Question for the knowledgeable folks on this site.
    Considering swapping out the offset/side shift boom on my pc75uu2.
    Reasons - I rarely use, and have not been in a situation in the last year where I had to have it - used it because It was convenient.
    Second reason is, I was going to start redoing the next stick pivot pin and cylinder pin and maybe the first shift joint.
    When I look at all the joints in that boom I am amazed that it still feeling as tight as it does!
    Helps that I redid all the pins and bushings on the bucket end last year.
    I have found a boom that is 12 inch longer pin to pin than the current boom.
    Pretty sure the length will not change the stability much - I would be losing 500 lbs off the boom just in the forward section of the current boom according to the weights given in the manual.
    300lbs on the knuckle, 135 on the side shift cylinder, 75 on the support rod, plus the big castings at each end of each section.
    I guess my main question is how does the extra boom length affect the actual digging force, lifting abilities etc.
    Any other concerns?
    Thanks for any insights!
     
  2. Bls repair

    Bls repair Senior Member

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    Does it have the computer controlled safety so you can’t hit the cab?
     
  3. Batkom

    Batkom Well-Known Member

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    Yes - it has all the parts - but was disabled when I bought it, and I went ahead and removed all the wiring wiring from the potentiometers, cleaned the wiring loom up and have put it in a box. Did not want to deal with it - I am the only one who runs it.
    That is the other thing I was thinking - a foot longer boom may keep the bucket from ever having the opportunity of getting in the cab.
     
  4. Batkom

    Batkom Well-Known Member

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    95E56D5D-B737-46B0-96F2-6993C02EFB81.jpeg Well the conversion is started!
    A Komatsu PC90-1 is the donor boom.
    Uses the same width at the boom base and the same pin diameter.
    It is 12 inches longer, and as close as I can calculate 470lbs lighter.
    The cl of the boom pin to the cl of the boom cylinder mount are also the same, however the pin holes in the boom are larger, so I put bushings in those.
    Worksing on rebending the steel lines on the boom now, and then will get hoses made.
    Will update when I am further along.
     
    Coastal, John Shipp and Pixie like this.
  5. Batkom

    Batkom Well-Known Member

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    5ABBE046-9B21-496F-8824-5F3F14E9CC44.jpeg 9FC01145-6008-4D57-B9C3-AE024EF5E61A.jpeg Got steel hydraulic lines reconfigured
    And added steel lines for the thumb.
    This was more work than anticipated!
    But came out well.
    Just need to clean up n paint.
    The guy that was helping me suggested we purge the original lines with the gas from the mig welder tank while heating and bending them to keep the scale out of the inside, seems to have worked well.
     
    Coastal likes this.
  6. John C.

    John C. Senior Member

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    The stuff is all seamless tubing without any coating so you shouldn't get any scale at all. Anything in them will come out in the return filter and it's more likely to be dirt than any metallics.

    Nice looking job by the way. What did you used to bend the tubing?
     
  7. Batkom

    Batkom Well-Known Member

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    The new lines were bent with a very nice tubing bender that my buddy has, not sure on the brand, has dies up to 1inch, and you crank a handwheel- has three speeds depending on the gear reduction needed for the size tubing you are bending. Also has degree indicator to help you get the bend angles you are after.
    It went well, but still took a lot of time by the time I made all the brackets.
    Thanks for the compliment.
     
  8. Batkom

    Batkom Well-Known Member

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    1A04E10A-A567-447C-95C7-29ECCC813AAB.jpeg BA8FEF55-912D-4567-9505-7CE229E61066.jpeg E11125BA-7CC5-43BD-8383-2342CEBAAFAE.jpeg 250C0A17-BEE3-43AE-AB94-9E5C26571C14.jpeg Well it’s finally out of the shop!
    Seems like projects like this are never ending- always something else you see you need to do.
    But snows gone and frost around my place is mostly gone, so time to put it to work.
    Put all new seals in the arm cylinder, painted boom, added led lights to the boom, also installed some flush mount leds to the house.
    The only thing I am a little concerned about is the height of the arm cylinder mount location on the arm.
    The cylinder bottoms out on the top of the boom just before it’s all the way in.
    So I am planning on cutting the end off and raising it a couple inches in the near future.
    It’s usable as is, but have to pay attention- not something I want to have to deal with long term.
     
    John Shipp and Tinkerer like this.
  9. Tags

    Tags Senior Member

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    Good job, looks great!
     
  10. John C.

    John C. Senior Member

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    Nice job. I've seen the cylinder issue on long sticks in the past. I usually cut off the cylinder base bracket and moved it back enough that the barrel didn't hit on the boom.
     
  11. Batkom

    Batkom Well-Known Member

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    Thanks guys!
    John C.
    So by moving the cylinder base bracket back you are making it so when the cylinder is extended it is at the end of its travel before the barrel goes low enough to hit the top of the boom?
    One thing that concerns me about raising where the cylinder rod end mount is on the stick - it will increase the leverage force.
    Which may not be a good thing as the arm was not designed with that in mind.
    But I guess if it breaks- I can find another one!
     
  12. John C.

    John C. Senior Member

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    When I move them back it lost some close up curl. The bucket wasn't able to touch the from of the track frames and the boom wouldn't set down as low when putting it on a trailer on the truck. When I loaded them on a trailer for them to be moved I pulled the cylinder to stick pin and the boom was able to settle all the way down. After the first two I guess someone complained to the engineers who designed the fronts and I never got another one.
    In looking at the distance between the boom pin and the stick to cylinder pin it looks to me like it is short from what I'm used to. It may be the angle of the photo but you might check it against a machine sitting in a lot somewhere.
     
  13. Batkom

    Batkom Well-Known Member

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    I agree John, it is short.
    The way the cylinder mounts on the offset boom, the cylinder follows the stick angle as it goes in n out, so it doesn’t need to be as tall.
    But with this conventional style boom mount location, it really does need to be taller.
    Planning on rainy it 3 inches.
    But will try and find some similar size machines and measure them
     
  14. John C.

    John C. Senior Member

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    Raising it I think should take care of the issue of the barrel hitting. It will be interesting to hear the difference in length between the boom to stick pin and the stick cylinder to stick pin and the stick to boom cylinder pin.

    Nice work!
     
  15. Coastal

    Coastal Senior Member

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    Cool! There's lots of uu machines for cheap that guys pass on because they are different. Good to see this swap! The orange confused me for a minute though!
     
  16. Batkom

    Batkom Well-Known Member

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    Yea, not fond of purple/Blue!
    And Komatsu Yellow just looks anemic to me.
    So I picked Allis Chalmers orange!
    Still need to paint the bottom frame, but it’s low priority as it’s always got some dirt on it.
     
  17. Batkom

    Batkom Well-Known Member

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  18. Batkom

    Batkom Well-Known Member

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    Have not figured out how to use that quote function correctly- only the first paragraph is John C !
     
  19. 007

    007 Well-Known Member

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    Nice job, I would never own a knuckle boom machine, the resale here in aus is not good ether so worth all the work i think.
    Just how much is the cylinder hitting the boom?
    Roughly what distance would the cylinder pin have to be moved so the cylinder just missed?
    The only reason i asked because u could make a couple of custom offset bushes for the cylinder ends that could easily lift 125tho both ends.
     
  20. Batkom

    Batkom Well-Known Member

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    The cylinder has approximately 3 inches of travel left when the barrel cylinder touches the top of the boom.
    So from what I can figure, I need to raise it a minimum of an 1 inch to clear the boom at full extension.
    I was going to do exactly as you suggested - make a 1/4 smaller pin on both ends and make offset bushings.
    But looking at the geometry it was not going to be enough of a change to keep it from hitting.
    The easiest option really would have been to find a cylinder with a little less travel rather than using the PC90-1 cylinder.
    But I had this cylinder already.