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Komatsu PC50MR-2 Slow Swing

Discussion in 'Excavators' started by zigblazer, Apr 6, 2022.

  1. zigblazer

    zigblazer Member

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    Location:
    NE MN
    I just purchased this Komatsu Excavator. I noticed the swing speed was a little slow. Measured and it is about half the rated speed. Did some research and found the swing and blade are driven off the same section of the pump. Checked the pressure and found the swing at 12Mpa where the spec is about 20Mpa, and the blade gets up to 15Mpa where the spec is almost 22Mpa. From what I've been told, these pumps rarely just get weak, they tend to work or fail catastrophically. Not sure how true that is, but have heard it from several people. I also find it unlikely that the pump can build up to 15Mpa for the blade, but only 12Mpa for the swing. I believe the problem lies elsewhere. All other pressures measure good. All other speeds seam normal, I didn't actually follow the testing procedure for those.

    I tried to locate the swing/blade pressure relief valves, and narrowed it down to two that I though possible. The Shop Manual shows a picture that is unhelpful. I can positively identify the main relief valve for the main hydraulic section. I removed and cleaned the two valves I thought likely. I saw no indication of contamination. I tried adjusting them each a full turn, which should have given a clear increase in pressure, but my swing and blade pressures remained the same. The swing motor has it's own relief valve (which is how it lowers the pressure down to 20Mpa) so I didn't bother checking that because it wouldn't affect the blade. Either neither of those valves were for the swing/blade or that is not the problem. The only idea I have left, is a restriction in the suction line, possibly the inlet screen in the tank. I will drain the tank, clean the screen, and put in a new hydraulic filter when the new filter and oil arrives.

    I have a background in auto and med/heavy trucks. I have a full understanding of hydraulic system theory, but very little hydraulic system experience beyond repacking cylinders, replacing hoses, replacing pumps, and changing filters. Does anyone have any other ideas of what I could check? Or maybe point me to the correct swing/blade relief valve.

    Thank you,
    Jeremy
     
  2. uffex

    uffex Senior Member

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    Good day Jeremy
    From my information you have two main control valve sections on the machine the smaller of the two controls both blade - swing & offset, I would agree with your diagnostics low pressure on one ought to be the same as the other. Clearly it is not the main relief as from what I gather it is in both directions would be more inclined to consider the refill valves in the motor head. testing creep by manually forcing the swing could confirm if this is the case. Attached some trouble shooting tips maybe of help.
    Kind regards
    Uffex
     

    Attached Files:

  3. zigblazer

    zigblazer Member

    Joined:
    Oct 25, 2016
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    Location:
    NE MN
    Thanks for the help.

    In-case anyone was wondering, it was the gear pump. I tested and cleaned many parts, with no change. Finally took a chance and just ordered a new gear pump. Took a while to find the correct parts diagrams (mainly because I wasn't familiar with the komatsu part lookup), and they couldn't find it at the dealer. Dealer could only find complete pump assembly available. They have rebuild parts for the main pump just couldn't find the part numbers, but the gear driven pump on the end does not have rebuild parts available. It drives the swing, blade, and control circuits. It was easy to replace, and I noticed a great increase in response from the other controls and faster swing right away. Pressures were right at 20mpa and 22mpa like they should be. Not sure what would make the blade pressure get higher than the swing with a weak gear pump, maybe it couldn't produce the flow? But it is all good now.
     
    uffex likes this.
  4. zigblazer

    zigblazer Member

    Joined:
    Oct 25, 2016
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    Location:
    NE MN
    If anyone was wondering, these excavators use a main piston pump with two separate output lines to run everything except the swing, blade, and control circuits. The swing and blade are run by a gear pump through the main pump housing. The control circuit is also run by the gear pump, but off the gear pump itself.
     
  5. wes allen

    wes allen Member

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    May 12, 2022
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    Location:
    san diego
    Hey zigblazer, I just got a pc40mr-2 with very similar problem. Where did you find the gear pump or schematics at? any help would be greatly appreciated!

    Thanks in advance,

    Wes
     
  6. uffex

    uffex Senior Member

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    Good day
    Parts for gear pumps are rarely made available as the pumps are so low cost where as piston pumps are more expensive. Gear pumps are available from many manufacturers. You need the gear size and the shaft and mounting details. This will give you an open market to explore. If I can help you more please drop me a line.
    Kind regards
    Uffex
     
  7. wes allen

    wes allen Member

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    Thanks for all your help, I believe its part #8 in the diagram im posting? Its listed as a pilot pump or am am on the wrong part? Thanks again!
     

    Attached Files:

  8. uffex

    uffex Senior Member

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    Good day Wes
    The pilot pump failure would affect all circuits not the slew/swing alone, I will try to find some information relative to your pC40 and come back to you, meanwhile keep your bucks in your pocket.
    Kind regards
    Uffex
     
  9. uffex

    uffex Senior Member

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    Good day Wes
    I have only dash 7 schematic but I would gamble it is the same and you are correct both blade and slew are driven from the so called pilot pump. I suggest you make the following check before you condemn the pump.
    Connect a pressure gauge to the "G" port of the two spool block, with full engine revolutions dead end the blade you should see about 3000 psi. Next this is important shutdown the revolutions to idle. If the pressure drops more than 300 psi. you have a internal leak. That could be a pump - relief valve - or leaking circuit.
    Carry out the same process operating the blade in the opposite direction. Dig the bucket in the ground and test again the slew in both directions, a loss on all circuits would indeed condemn the pump.
    I hope that is of help.
    Kind regards
    Uffex
     
  10. wes allen

    wes allen Member

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    Thank you so much for your help!
     
  11. wes allen

    wes allen Member

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    I was only getting about 1600psi on the test today at full revs and only 1000 psi at idle from the outlet port. I ordered a new pump. Got a decent deal on the machine hoping the pump will take care of it. Thanks again for all your help.
     
  12. wes allen

    wes allen Member

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    Also, does anyone have the torque specs for the bolts attaching it to the main pump or a link to buy a shop manual?

    *Edit* Purchased one, thanks again for everyone contributing to this site!
     
    Last edited: May 15, 2022 at 11:00 PM
  13. uffex

    uffex Senior Member

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    Good day Wes
    Take some prcaution with the fluid getting it checked for contamination remember to change those filters. Bleed the pump and run at idle for 20 mins. this will flush out any ingress before you make it work under pressure.
    Kind regards
    Uffex
     
  14. wes allen

    wes allen Member

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    Read that last post a little late, was very carful about contamination and changed to a new filter, didn’t bleed it but ran it for a few minutes at idle before testing..


    It worked! New pump and it swings right at spec again. The blade and other controls seem to be more responsive as well.

    One question, I didn’t see any mention of locktite or thread locker on the bolts, all my marine engines require it but is it not needed for these. I did torque to spec.
     
  15. John C.

    John C. Senior Member

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    A properly torqued bolt used in the proper application will never come loose. Komatsu engineering is pretty good about that.
     
  16. uffex

    uffex Senior Member

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    Good day
    I suggest you only use thread lock when recommended frequent use may only cause issues later, previous post relates to tests made, the simple steps prolong the life and performance of the pump.
    Kind regards
    Uffex