KX91-2 hydraulics

[rbt4714]

Hello everyone. I just purchased a Kubota KX91-2 and it runs well and all functions seem to work, the only problem that I can see at the moment is it needs new tracks.

I tried to lift the tracks off the ground to check the condition of the lower rollers. If I lower the dozer blade all the way and then swing the cab 180 degrees and try to lift the machine off the ground with just the boom it barely gets the tracks off the ground up but if I use the combination of the stick and the boom it lifts it completely up with no problem.

If I do it the other way around, lift the machine with just the boom and then try to lift the other side with the dozer blade I have the same problem. The dozer blade only barely lifts the tracks off the ground.

My question is, is this normal or do I have a hydraulic pressure problem?

 

[rbt4714]

I think I have my answer that I found on previous older thread in this forum.

https://www.heavyequipmentforums.com/threads/should-mini-digger-lift-itself.20223/

From gpap123

"Note that the force that is going to raise the machine up, has to be vertical. So you need two movements, boom down and stick open. Hope that helps!"

And that is exactly what I have to do in order the lift the machine way up entirely off the ground.

I would still like to hear from other Kubota KX91 owners to see if their machine requires the same procedure.

 

[code54]

I have a 91-3 and use both functions to lift it. Don't know if I ever tried only one, but with both it lifts right up

 

[code54]

Just checked mine for you - can lift it up easily with one function. (boom down)

 

[rbt4714]

Just checked mine for you - can lift it up easily with one function. (boom down)

I don't know how that's possible unless you adjusted some of the pressure relief valves to a higher level.
The arm (stick) force is only rated at about 3600 pounds so I can't see how the boom force is much higher than that. And even if it is higher, it's probably not as high as the weight of the machine which is about 7600 pounds.

To be clear, mine will easily lift one end of the machine all the way up (front or back) with just the boom with the dozer blade up but NOT with the dozer blade all the way down. In other words, with the stick situated perpendicular with the boom, I can lift the machine up as far as the boom will go down tipping the machine way back. But after doing that, I can not lift the other end of the machine all the way up off the ground by pushing the dozer blade all the way down. It will not fully extend the dozer blade cylinder out to its full limit without triggering the pressure relief valve.

And vice versa, if I first lift the machine up using the dozer blade, it will lift up the front end all the way up to the limit of the dozer blade cylinder at its fully extended limit. Then if I swing the cab around 180 degrees, the boom cylinder will not fully extend out to its limit. I need to use both the boom and the stick to get full extension of the boom cylinder.

 

[code54]

OK, I follow you now. I was just lifting one end without any real effort. When I drop the blade and lift the machine, then I use two functions to lift the rest of the machine off the ground. If the other end is already up, the blade does not have any problem lifting the machine off the ground. (Everything is stock and I have less than 300hrs on the machine)

 

[rbt4714]

OK, I follow you now. I was just lifting one end without any real effort. When I drop the blade and lift the machine, then I use two functions to lift the rest of the machine off the ground. If the other end is already up, the blade does not have any problem lifting the machine off the ground. (Everything is stock and I have less than 300hrs on the machine)

What happens if you first use the dozer blade to lift the front up fully and then swing the cab around and with the stick perpendicular to the boom, just use the boom hydraulics without using the stick or bucket hydraulics? Will the boom cylinder fully extend out without triggering the pressure relief valve and thus lifting the machine way up off the ground?

 

[rbt4714]

OK, I follow you now. I was just lifting one end without any real effort. When I drop the blade and lift the machine, then I use two functions to lift the rest of the machine off the ground. If the other end is already up, the blade does not have any problem lifting the machine off the ground. (Everything is stock and I have less than 300hrs on the machine)

Or with the boom first fully extended down lifting one end way off the ground, will the dozer blade then be able to fully extend down thus lifting the other end of the machine way up off the ground so that the tracks are parallel to the ground?

 

[code54]

Or with the boom first fully extended down lifting one end way off the ground, will the dozer blade then be able to fully extend down thus lifting the other end of the machine way up off the ground so that the tracks are parallel to the ground?

Yes- if I lifted the other end first the blade will lift the tracks right up in the air, all the way to the top of the blades downward travel.

 

[rbt4714]

Apparently the newer models are different because I had someone who is selling a KX91-2 just like mine make a video and it does exactly the same thing as mine.
Either there is something wrong with my machine and this one or they are not designed to lift both tracks completely way off the ground using just one hydraulic function.

 

[mikebramel]

Bore surface - rod surface x pressure x geometry

 

[rbt4714]

Bore surface - rod surface x pressure x geometry

Not sure what you're getting at but here's a KX91-3 (slightly newer model) that has no problem lifting itself up with one hydraulic function.

Same engine/horsepower, same three hydraulic pump setup, same size hydraulic cylinders etc.

My guess is the pressure relief settings are out of adjustment on mine and the other KX91-2 in the previous video.

The reason I think that is because mine has massive digging power to the point it literally will load the engine down then you get that familiar loud squeal when the pressure relief valve finally kicks in.

On the other hand when I use a combination of stick and boom to lift one end off the ground and then use the dozer blade as in the video above, it won't lift the machine off the ground. The pressure relief valve kicks in way too soon, barely making a squeal and the engine is not loaded down whatsoever.

Looking over the hydraulic schematic, there are a total of 9 adjustable pressure relief valves on the control valve assembly. Two of which are used for the boom. One to limit pressure when extending boom cylinder (lifting/digging) and one to limit pressure when retracting boom cylinder (pushing downward to lift machine off the ground).

There is only one for the dozer blade and that is for limiting the pressure when extending dozer cylinder (dropping blade to lift machine).

According to the specs, all three of them are to be set the same or just under 3500 psi. Not sure how this is done since the 3 main pressure relief valves for the 3 pumps are set lower. Pump 1 and pump 2 (for travel, arm, boom, bucket) just over 2900 psi and pump 3 (for swivel, swing, and dozer) just under 2300 psi.

 

[code54]

The last video is exactly how my 91-3 works.

 

[rbt4714]

The last video is exactly how my 91-3 works.

It's merely a function of pressure relief valve settings as the KX91-2 and KX91-3 are nearly identical in horsepower and hydraulic specs.