Backhoe Help with Kubota KX121 Mini Excavator

[Viat]

I have some questions about operating a new KX121 mini excavator since I could not find anything relevant in the manual. I've rented a smaller Kubota mini excavator before and don't remember having these issues.

-When digging I put the dozer blade firmly into the ground in front of me (to the extent that it slightly lifts the machine up). When I try digging the arm pulls against the dozer blade and causes the dozer blade to raise up so that it's no longer supporting the unit in the front (the hydraulic cylinder is retracting on the dozer blade). Is that normal?

-When digging and pulling up with the arm against hard ground my bucket actually ends up curling outward without any of the bucket controls being touched. The hydraulic cylinder is retracting from the pressure on it. It seems to be similar to the issue with the dozer blade. Is this also normal or is it the same issue as above?

-When digging in hard ground the arm just stops moving because it's not strong enough. However, I don't hear the engine sound change at all -- I would have expected it to grunt/slow down. Is that normal? I originally had a 24" bucket on, and then moved down to an 18" but I'm still experiencing the same issue of having a very hard time digging -- the ground is very dry dirt but it's not clay or rock.

Is this expected behavior? Are there relief valves on the hydraulics that could be configured wrong? Should I be looking for hydraulic leaks?

Thanks

 

[Tags]

There could be relief valve issues but it almost sounds like you may be trying to dig more than the machine is capable of handling. My 161 blade will go into relief and do what you describe if I am trying to do to much with it, but if I'm trying to do too much with the bucket, boom, or stick the engine will typically bog before/while going into relief. Also, is the machine brand new or just new to you, if its brand new maybe the dealer should check it out, but if its used how many hours are on it and what did the previous owner do to it maintenance wise, or have the relief valves been fooled with?

 

[jdfire]

I'm not an expert on hydraulics, but I don't think the relief valve would allow the cylinder to retract. The relief valve bleeds off EXCESS pressure but the full rated pressure should still be available to hold the cylinder in place. I wonder if it's an issue with fluid leaking by the seals either in the valve or the cylinder.

 

[radioman]

I'm not an expert on hydraulics, but I don't think the relief valve would allow the cylinder to retract. The relief valve bleeds off EXCESS pressure but the full rated pressure should still be available to hold the cylinder in place. I wonder if it's an issue with fluid leaking by the seals either in the valve or the cylinder.

I concur-- I dont think you have a single issue here - but rather it was abused before you got it. I question it that its new or its new to you? If it really brand new - you would be contacting the dealer already as it sounds like a warranty issue.

 

[Viat]

It's brand new and has 11 hours on it now. I will ask the dealer about this and post my results. I've been digging with it slowly with the angle blade behind me (that way I dont have to readjust it constantly).

Thanks for the info.

 

[mike69440]

I'm not an expert on hydraulics, but I don't think the relief valve would allow the cylinder to retract. The relief valve bleeds off EXCESS pressure but the full rated pressure should still be available to hold the cylinder in place. I wonder if it's an issue with fluid leaking by the seals either in the valve or the cylinder.

If you overload a cylinder it will retract, but the relif settings on the above machine sure seem weak.

 

[boggen]

being new, have you checked all your oil levels? just wondering if maybe oil was put in, but the actual cylinders never operated. and then oil levels never rechecked after some use of the machine as air was worked out of the hoses and cylinders, resulting in a low oil level, and air in the cylinders and hoses still.

air can and will compress unlike the hyd oil. and i am assuming you have some air in the cylinders and hoses.

dozer blade moving up once you place some force on it. air in hoses / cylinders compressing.

as you pull up and bucket begins to move on its own. the air is expanding on one side of the cylinder and compressing on other side of cylinder.

i would imagine if you knew if relief valve was opening up, due to the hissing / noise, or whistle like sound they can make. but not always pending on were muffler / engine is in relation to your ears.