Kubota Hydraulic Pump Leak

[Beckbenj]

Hi All,

I’m trying to get an idea on how to tackle a small hydraulic leak I’ve noticed on one of the ports of my Kubota KX161-2 main hydraulic pump. The fluid is coming out between the jam nut and set screw which is in the side of the pump body (see attached picture). Looking at the cross section diagram I’ve found for the pump, I don’t see any type of seal on the set screw itself. Should the set screw have a seal of some type? I was considering adding thread sealant to the set screw and reinstalling.

 

[Coaldust]

The RD201-69480 O-RING is leaking. There is a piston looking doohickey under that cover. It has an o-ring, which is probably the culprit. Look at the parts diagram again and it will make more sense.

There isn’t supposed to be oil under that cover. The set screw pushes on that piston. Which Kubota calls a bushing in the parts diagram.

Don’t touch that screw.

 

[Beckbenj]

I haven’t been able to find much about the function of the set screw, but it seems to control pump stroke / pressure. Does that sound right?

I was looking at the parts diagram last night. You’re referring to oring 510 that fits into piston 520, correct?

To fix this the hydraulic tank needs be drained it looks like? Is it as straightforward as pulling the piston out and put a new oring on it?

 

[Coaldust]

Yes. Min and max pump stroke.

I would be tempted to remove the pump and do the work on a bench. It would be easier to keep things clean that way

 

[Beckbenj]

Yeah I’ll look into taking it off the machine, seems easy enough.

 

[Coaldust]

Good luck. Let us know how it turns out.

 

[Beckbenj]

I’ve ordered the o-rings for the repair but will be leaving the pump on the machine as the trunion cover (#480) is readily accessible. I’m also hesitant to pull off some of the suction and pressure tubing for fear of opening a can of worms.

Being relatively new to heavy equipment, does the hydraulic tank need to be drained completely to do this repair or does the pump provide some restriction to where some fluid would drain, but not like a fire hose? My other thought was using the “shop vac on hydraulic tank fill port” trick to hold back the fluid while I repair may work as well.

 

[Coaldust]

It will leak like crazy. The vacuum trick will probably work fine. I use a transducer, myself. There are some threads that discuss both ways.

 

[Beckbenj]

I've finally gotten around to replacing the seals. A pretty straightforward job. The o-ring seals were definitely hard and compression set.

The vacuum trick didn't seem to be enough to hold back the flow so I ended up draining the hydraulic tank (needed to do anyway).

Is there any priming of the hydraulic pump that is needed before restart? I would assume refilling the oil tank would cause the pump to fill by gravity since it is below the level of the tank.

 

[James Sorochan]

Not sure if yours has one but our 121-3 has a fitting that I had to bleed the air out of right on top of the pump.

 

[Beckbenj]

Is this the plug you’re referring to?

I’m trying to find the procedure in the service manual I have but haven’t located yet.

 

[James Sorochan]

Yes, that's it. I cracked mine open after I filled up the hydraulic tank. Start it and let the machine run until you start to get a steady stream of oil. It says in the manual to let it run for a few minutes before you move the hydraulics. Once you figure the air is purged tighten plug and slowly engage the functions listening for cavitation. If its cavitating you will hear it. In that case crack open the plug again while its idling to purge out the air. It took a few minutes to work the air out of mine.