BX23 HST Oil Leak

[RStricker]

I have a 2005 BX23. For quite some time it has been leaving a little trail of hydraulic oil that drips off the bottom under the HST. I have searched to no avail; I finally found a mechanic who understands small Kubotas and he spent the time to find the problem. There's an opening on the top of the HST. Open to the air. It's a place for an oil filter to be mounted (apparently the HST is used on a variety of different equipment, and in other configurations this is where the oil filter is mounted.) But in this equipment, the opening is directly under the seat support bracket. My mechanic found that after running for a little while, oil would start slowly flowing out of this opening, and ends up on the ground under the tractor. I checked the parts diagrams - Kubota shows this as being open; there is no plug. Note that I have checked the little red-cap breather behind and below the seat. It is not plugged.

First question: Does anyone understand what may be happening here to cause the oil to flow out of the top opening in the HST?
Second question: Do I run any risk by putting a plug in the hole on the top of the HST?

 

[rScotty]

Can you post the parts diagram. I cannot find that port on Messicks.com. There is a chance that it is just missing a plug or something similar like a hole tapped too deep.

But when this happens it is almost always either a breather that is plugged. Another thing that happens is water got into the hydraulic oil - turning it into milky fluid which is now it is foaming.

But check the breather first. It is common for Insects fill them with mud.

 

[RStricker]

Attached is a copy of the parts diagram (Messick's page D01000 HST, also shown on D01500 HST). I found no evidence that Kubota intended for there to be a plug here.

I pulled the breather out and confirmed that it is not plugged, air will pass thru it. And, the oil is clear. There's no water in it.

 

[rScotty]

Then it is sounding like the same basic casting was used in several versions but not finish-machined for yours - or maybe not for any BX23. So is yours maybe an oops or thin casting?

Filters have two paths; Is it leaking from the center or outer? You might not be able to tell....but if the center is threaded, that internal thread normally used is a tapered thread in BSPT or NPT. You could put a plastic pipe plug in the center if threaded.
The same idea would seal the outer but would need more fab work and an O ring.

Either way, if oil can get out then water can get in...so good to seal it up. Too bad there isn't room for a filter, but fab shouldn't be too hard even if you have to use a filter as a template.

 

[RStricker]

It does not appear to be a casting defect (at least from looking at the outside). And it's leaking from the center. It appears that the internal threads are the same as for the hydraulic oil filter used on this model, and a few caliper measurements confirms it. Brave AI tells me that Kubota oil filter #HHK20-36990 has a threaded opening size of 3/4-16 UNF. I'm going out today to pick up a bolt this size to be used as a plug, along with something to use as a gasket under the head. And btw, I already tried the PVC plastic plug in this opening. There's enough heat to cause the PVC to relax and let oil seep right by the threads.

 

[5030]

Don't forget to put a sealing ring (copper or rubber) under the head of the bolt before screwing it in or it will continue to leak.

 

[rScotty]

Sounds like you are on top of it. Most internally threaded tapered threads on Japanese castings are British Standard tapered thread and not NPT. And there is an interesting historical story behind that.

But if there is an exception to most being British Standard, I would not be surprised to find that it is in the oil filter mounting nipple. Note that most oil filters have internal threads that fit over a short piece of pipe threaded on both ends. Often both ends have a tapered thread. But maybe yours is UNF on one end and oll filter thread on the other.....though does that really make sense?? Might want to check first before forcing something in there.
If the missing spud is really a tapered thread and you end up forcing it, then consider using sealer and leaving it there once it is in place.

 

[mossycreekoutdoors]

Yours must have a hole or crack in the housing. While that is semi machined for a filter it is not completed and should not be open in the threaded area or outside area. Ive removed many of those and they are all sealed there


Daryl
Mossy Creek Outdoors
Www.mossycreekoutdoors.com

 

[dicktill]

Sorry to hijack the thread, but a related question: Are these hydrostatic transmissions "flooded" with just an overflow back to the tank/sump/reservoir/transmission casing?

TIA

 

[Redlined0002]

Sounds like you are using the wrong oil in it. Buy the Kubota oil design for your unit.