BH90 dipper stick piston bent or broken

[jmc]

A good design should anticipate any reasonable use. Putting full hydraulic pressure on the hoe in ANY position is a reasonable use and the rod should not buckle. They have a design flaw. On the other hand, if you were hammering with it...

John

 

[JWE]

You are not alone with this problem. I contracted a plumber a few months ago to dig up a water line and he used a BH90. He told me that his only complaint is that it keeps bending dipper sticks. He also has gone through three of them.

 

[john_bud]

Does anyone have the diameters of the cylinders and the rod diameters? I am just curious as to how big they are.

Also, one post listed a repair at around $700 for one cylinder. WOW, that's highway robbery. If you have a cylinder go bad, check with
surpluscenter.com. They carry used as well as new hydraulic cylinders. You can replace the cylinder with new for $300 or less.

Just a different way to go...

jb

 

[JoshJ]

Just my two cents:

1. Just skimming through, but a larger diameter rod will not create less force on the extension part of the cylinder, which is more likely a cause than the retraction motion. It will, though, resist buckling better

2. If it bends while moving that cylinder: A relief valve setting could make a world of difference. Granted, when digging close in the cylinder rod is extended further and more likely to bend, but this should be accounted for in the relief valve. Isnt that the point of it?

3. If it is bending when using other functions:
I am assuming that backhoe hydraulics do not drift, and thus employ some sore of check valve. If so, then there is no "static" protection of your cylinder. What I mean is, you can apply a force on the dipper stick cylinder with another function that is larger than you could apply by moving that cylinder. For example, if the dipper was close in, and you were pulling up with the boom and got caught, a large force would be applied to the cylinder (because the fluid in it cannot leave) that could possibly bend it. This is difficult to "engineer" prevention for, and it sounds like it could be the problem The best thing to do would be to avoid situations like this by having the dipper swung out past vertical. Sorry to hear about your misforture, though.

 

[Bob53]

I checked mine and it does have the stop plate also, I guess I'll e-mail Kubota to see if they think it would help if removed.
then i read another one with 3 dipper cylinders broke. Seem like they could have designed a little better if this many problems with this cylinder. At this point I'm not so sure mine broke when fully extended. The 1st time it actually broke in half inside the cylinder.
Johnbud, the cylinder new was $540, then delivery and installation. I would have never taken to dealer if did not think warranty, i thought i'd just be paying delivery and installation cost.Its easy enough to change out myself. Next time I'll just get it rebuilt and another type. With all the problems with Kubota cylinder, can't hurt to try another type. Well still got another year on warranty so probly good i got the Kubota cylindar, something else goes wrong on hoe, they'ed just blame it on my non kubota cylinar if not exactly the same ??? Hopefully i won't get to try another cylinder though.
Thanks for the pictures enumclaw, stick with that dealer of you'res, wish mine was as coopertative.

 

[L3400]

I bent and broke the same piston on my BH75 last week. After reading a few posts and recreating what I was doing, I came to several conclusions. 1) I was working in a crowded position with the piston extended. 2) I measured the piston length and it was apprx. 4-5" longer. 3) As you should not pull stumps with the boom fully extended, ( from manual ), I will no longer work in a crowded position. 4) My dealer told me that Kubota had a problem they were aware of and took care of me immediatley. 5) The new piston is only slightly longer fully extended. 6) I marked the boom and dipperstick so that I am aware that the dipper is fully retracted. Good Luck!!

 

[enumclaw]

Hi Bob53. A couple thoughts on the stop plate. With the stop plate completely removed as on my tractor, if I accidentally back into something, with nothing to stop the dipper stick but the piston, the head of the piston would be rammed into the top of the cylinder. So I need to be careful of even a small bump. If I were going to grind down the stop plate, I would grind until the piston can just be fully extended. Then the piston would still have some protection. My other observation was that with the boom in the upright position, traveling pin in and bucket curled up, after a day, leakdown in cylinder allowed the the bucket to uncurl and the teeth contacted the boom. So, I have to be careful to extend the dipper stick a bit before I open the bucket to prevent scraping the teeth across the boom. So, there is a reason for the stop plate. I'll be interested to hear what you do.

 

[enumclaw]

Hi john_bud. According to my manual, the piston rod diameter of the dipperstick is 1.38" and the cylinder bore is 2.56". For the first rod that broke, I was quoted a price of $600 for the piston and $700 for the complete cylinder. The quoted price of the new, improved cylinder was $1300.

 

[enumclaw]

Hi L3400. My BH90 manual made no mention of pulling stumps in any position. And in fact, the three times my dipperstick piston rod broke, I was never pulling stumps, only light duty. Thanks for your observations. I too will be much more careful when the dipperstick is in close but with these small backhoes, where you can't move without getting off, pulling up the stabilizers, getting on the tractor, pulling ahead, getting off, putting the stabilizers down, etc So, you try to get as much done in current position and hence work in close. I really believe that breaking rods is a design problem and that the rod should be larger. I was told that there is not a pressure relief valve in the cylinder, only bypass mode which I think occurs only when the piston is fully extended.

 

[Bob53]

enumclaw,

Not much else i can do about the stop that you're dealer removed. Just talked to my dealer and said he cannot remove it with no bulition on the BH75 and if i removed or ground stop down to fully extended , I could volid future warranty depend on how some part on hoe failed. So I'm kinda stuck for another year here before i try and improve some way. Like you said with so many failures design has to have some part in it. I did e-mail kubota a week ago about the problem but got no responce. I'll try e-mailing them one more time.