BH75 Piston broke, twice! Design problem??
- Thread starter Volnavy
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Henro
Elite Member
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- Few miles north of Pgh, PA
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- Kubota B2910, BX2200, KX41-2V mini EX
<font color="blue">I don't know what your digging style is, but the closer you dig to the unit, the higher the chance of bending a cylinder. </font>
Jerry,
Why would that be?
It just seems to me that the beauty of hydrauilcs (if properly designed) would be that the cylinder would just reach the end of its stroke and stall there...or push until it was unable to overcome whatever resistance was oposing its movement, and stall there...Without anything being damaged, and without the cylinder damaging itself.
Personally, I would not want a hydraulic implement that would self distruct during its normal range of operation. Which is what push and pull would seem to be to me. Now side thrusts on a small backhoe is a different story, but I don't think we are talking about abuse here in this thread.
Are there some backhoes out there that do suffer damage to cylinders when operated within the design limits? I sure would not want one of those!
Jerry,
Why would that be?
It just seems to me that the beauty of hydrauilcs (if properly designed) would be that the cylinder would just reach the end of its stroke and stall there...or push until it was unable to overcome whatever resistance was oposing its movement, and stall there...Without anything being damaged, and without the cylinder damaging itself.
Personally, I would not want a hydraulic implement that would self distruct during its normal range of operation. Which is what push and pull would seem to be to me. Now side thrusts on a small backhoe is a different story, but I don't think we are talking about abuse here in this thread.
Are there some backhoes out there that do suffer damage to cylinders when operated within the design limits? I sure would not want one of those!
JerryG
Super Member
<font color="blue"> Why would that be? </font>
That is a good question and I have tried to figure it out several times over the years. But I have yet to formulate a good reason. I know that I have seen many BHs with bent cylinders, just like this one and almost all of them have done so while digging close to the machine, while trying to get the last little bit possible.
That is a good question and I have tried to figure it out several times over the years. But I have yet to formulate a good reason. I know that I have seen many BHs with bent cylinders, just like this one and almost all of them have done so while digging close to the machine, while trying to get the last little bit possible.
kubotabilly
Gold Member
Henro,
I agree with you. It should not matter if your digging 6 ft. from the tractor or trying to take that last scoop as close to the tractor as possible. I do it all the time with my Woods BH. There has to be a design flaw there somewhere.
Volnavy, get it to the dealer for a good going over. Get Kubota involved.
Bill
I agree with you. It should not matter if your digging 6 ft. from the tractor or trying to take that last scoop as close to the tractor as possible. I do it all the time with my Woods BH. There has to be a design flaw there somewhere.
Volnavy, get it to the dealer for a good going over. Get Kubota involved.
Bill
plants4u
Member
Volnavy,
Sorry to hear about the equipment problem. I have the same backhoe as you and your situation concerns me. Since I read your post i did go out and do some extra hard dipperstick digging just to see what may happen. I have not been able to accomplish the same. I wonder if it is possible that the dipperstick or pivot pin bushings are binding? My only issue has been breaking bucket teeth, but my unit has performed well for me. Hope your situation is resolved promptly, let us know.
Clem
Sorry to hear about the equipment problem. I have the same backhoe as you and your situation concerns me. Since I read your post i did go out and do some extra hard dipperstick digging just to see what may happen. I have not been able to accomplish the same. I wonder if it is possible that the dipperstick or pivot pin bushings are binding? My only issue has been breaking bucket teeth, but my unit has performed well for me. Hope your situation is resolved promptly, let us know.
Clem
I have had no teeth break and really have not been pushing it at all. WHen I put the new cylinder on I greased all the fittings very well so I hope there is no binding, however the dealer did use the same busing on the piston end, the lower end has none. I'll call them today and keep this thread updated with what I hear. It is good to know someone else has a BH 75 that is working properly.
bugstruck
Platinum Member
Henro, If someone were driving the tractor while dragging logs with the BH bucket, or something like that, I may understand it. I've done that on rare occasion with lighter trees and used mine as a hammer against a stubborn tree this past weekend but I had my dipperstick out (rod in). Maybe I'll ease up on that a little. I've run heavier equipment and never seen a rod bend like that. I'm sure it's happened though.
Seems to be a weak link on some of the Kubota hoes. The reason they are bending when digging in close is probably because thats when the rod is most extended, in compression, and most vulnerable. Per your comments, you shouldn't be able to bend a cylinder like that in any sensible digging operation. Looks like the curl cylinder is beefed up on the newer BH 90 according to the another post. I think that's what I have on my Dec 04 BH. However, I believe it's the dipperstick cylinder issue I've seen the most posts on.
/forums/images/graemlins/confused.gif
Seems to be a weak link on some of the Kubota hoes. The reason they are bending when digging in close is probably because thats when the rod is most extended, in compression, and most vulnerable. Per your comments, you shouldn't be able to bend a cylinder like that in any sensible digging operation. Looks like the curl cylinder is beefed up on the newer BH 90 according to the another post. I think that's what I have on my Dec 04 BH. However, I believe it's the dipperstick cylinder issue I've seen the most posts on.
/forums/images/graemlins/confused.gif
Darren
Veteran Member
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The rod has to be extended to get bent like that. As you said, that happens when the operator is working close to the machine. When the boom is adjusted so that the minimum amount of rod is exposed, it can withstand more force.
Think of it as a short beam as compared to a long beam. With the same load on both beams (as long as they're the same cross section) the long beam will show more deflection. The cylinder and rod is actually designed as a column but that's just a vertical end-loaded beam in a sense. Once you exceed the elastic limit of the steel, the deflection is permanent. In other words, it's bent for good.
Kubota obviously short-changed the design. Whoever did the design didn't realize the pressure relief valve would allow enough force to bend the rod when it was extended.
Think of it as a short beam as compared to a long beam. With the same load on both beams (as long as they're the same cross section) the long beam will show more deflection. The cylinder and rod is actually designed as a column but that's just a vertical end-loaded beam in a sense. Once you exceed the elastic limit of the steel, the deflection is permanent. In other words, it's bent for good.
Kubota obviously short-changed the design. Whoever did the design didn't realize the pressure relief valve would allow enough force to bend the rod when it was extended.
My BH manual shows a picture of someone pulling something with the BH and has a big circle and X over it. In other words that is a "no no".
Kubota is going to pick it up tomorrow and work on it. They said that the stops may not be adjusted correctly. Stops? I thought it stopped when it ran out of travel. Oh well, maybe I'll learn something. He also mentioned something about reducing the power. That worries me, I don't need it any weaker. I guess I could check the lift capacity when I get it back if I had weights that big. Can they really reduce the hydraulic pressure. This one is not PTO powered, it runs off the tractor hydraulics.
They also have a recall on the PTO so will fix that too.
I really wish I could finish digging my ditch. But it is supposed to rain the next three days, so maybe it'll be done by the time it dries out.
Kubota is going to pick it up tomorrow and work on it. They said that the stops may not be adjusted correctly. Stops? I thought it stopped when it ran out of travel. Oh well, maybe I'll learn something. He also mentioned something about reducing the power. That worries me, I don't need it any weaker. I guess I could check the lift capacity when I get it back if I had weights that big. Can they really reduce the hydraulic pressure. This one is not PTO powered, it runs off the tractor hydraulics.
They also have a recall on the PTO so will fix that too.
I really wish I could finish digging my ditch. But it is supposed to rain the next three days, so maybe it'll be done by the time it dries out.