BH75 Piston broke, twice! Design problem??

Junkman · Apr 11, 2005

Lessening the pressure of the hydraulics will resolve the bending problem but cause other problems. If you paid for a machine to do a task that requires 2000 PSI and they reduce it to 1500 PSI, so it won't bend there inferior cylinders, then it isn't worth the money that you paid for it. They should fix the defect with the correct part, not lessen the strength of the machine to match the weakest link. That is like buying a 8 cylinder car and removing 2 spark plugs, because it can exceed the speed limit on the highway. /forums/images/graemlins/grin.gif

ArkCivEngr · Apr 11, 2005

Tractorman,

Did you mean to say that they increased the dipperstick cylinder diameter by 10 mm? Surely they wouldn't think beefing up the other cylinder would fix the problem?

AntrimMan · Apr 12, 2005

Ark,
I think tractorman was refering to the BH90 bucket curl cylinder, not the dipper and not on the BH75.

Volnavy,
thanks for the photos. Was the broken piston rod hollow by any chance? Lowering the system psi would anger me if it is currently at the recommended setting. You might find a valving problem within the hoe control to be at least one of the issues here. The hoe should not rely on the system relief valve to open and if you think about it, it really can't work that way. There are two hoses from the tractor system connected to the hoe. One is supply, always at system psi, the other is a return always dumping back into the reservoir. The hoe valve must contain a blow-off to dump into the return. When a cylinder is overloaded it should simply open the blow-off. I think maybe this is one of the issues. I doubt you could get two weak cylinders by coincidence. That said, the cylinder just may not be up to the job, and if so, Kubota will be aware of the issue but in an early state of denial (replace customer cylinders until they have a fix). I'm certain they will make you whole, given time. And by the way, that buckling can happen with the rod fully retracted if the piston bottoms and the dipper keeps trying to push it farther in through externally applied dipper motion. That cylinder will then extend much more easily than it will retract due to the difference in area on each side of the piston. It may only extend once. As stated in a previous post, travelling with the bucket in ground contact will load the hoe hydraulics if a relief doesn't open (I'm don't mean to at all infer that this is what happened).
Good luck with the dealer, don't settle for less than satisfaction.
Please continue to keep us posted.
Thanks,
Martin

Volnavy · Apr 12, 2005

The piston was not hollow, I wish I would have taken a picture of it now.

I see what you mean about if the bucket hits the ground during transport, it could do damage. And I have had it contact the ground before when I went from level surface (road) to a bank. However, this last time it was fine when I started digging and 20 minutes later it was bent. But it is good advice, and something to think about when it is attached.

Volnavy · Apr 15, 2005

Well, They picked up the tractor yesterday. They came out with a group of service people and a design engineer, changed the cylinder, went up to where I was digging, took pressure tests, tested the soil, and who knows what else. I was not there.

My neighbor said they were all very nice and spoke well of the customer, wanting to provide top notch service. I was really impressed with what I heard.

I'm not sure they know the root cause of the problem, but they are confident that they will fix it, evenif they have to tweak the design (larger cylinder?).

I'll keep you all updated.

SkyPup · Apr 15, 2005

That is good to hear! /forums/images/graemlins/wink.gif

Volnavy · Apr 18, 2005

Well, I got a call from the Quality Assurance Engineer in their manufacturing plant in Gainsville GA. He and several others came up here to TN, put on a new cylinder and ran it through a bunch of tests, even trying to get it to break again; no luck. They do not know what the root cause of the failure is.

When I get it back I will set up a video camera to record myself trying to finish my project. If it breaks again, we should know what position it is in when it happens. I guess we are in a wit and see, fact finding mission.

Here is my best guess of when it can happen. Suppose you are digging the 4' ditch, and are digging close, and are pulling in and up with the boom and dipper stick. You look down and see that your bucket is not very full and you decide to go down for some more. Well, if you just extend the bucket back down, you would have a lot of leverage against the dipperstick cylinder. The leverage from the curled bucket may be enough to bend the dipper stick piston. I don't know whether to test this hypothesis or to try to avoid it.

I think it would be best to test it while under warranty rather than to get into the situation again and have to buy another cylinder myself. Of course, I could just be an engineer overting the problem. I'm gone the next few days but should have the tractor back when I return.

This is very frustrating. I paid 24K for a machine to do dig a ditch, to get power, to build a garage, etc; and have not had it the last three weekends. My project is getting way behind schedule.

Do I sound like Ramon49 yet??

ByronBob · Apr 18, 2005

You should have a warranty from the time they change it for a year past that. I'd just go about your business and if it fails raise helll.

Av8r3400 · Apr 18, 2005

I don't think it works that way. 1 Year from date of purchase on attachments as a whole, not the components as they are replaced. (Thats what my dealer told me concerning the FEL valve on my Kubota) /forums/images/graemlins/frown.gif

Volnavy · Apr 21, 2005

I got my tractor back, they cleaned it up, it looks new again, that was a nice touch from the East Tennessee guys here in Knoxville.

It looks like a good weekend, so we'll see if it breaks again. I'll set up my digital video camera and if it fails, I'll suppy a link to the video.

Wish me luck, I just don't know which kind /forums/images/graemlins/wink.gif

notamustang · Apr 21, 2005

Well I wish you the luck that I think is best /forums/images/graemlins/smile.gif
I hope it is fixed, flawless and works better than it did before!

jhb · Apr 21, 2005

( Here is my best guess of when it can happen. Suppose you are digging the 4' ditch, and are digging close, and are pulling in and up with the boom and dipper stick. You look down and see that your bucket is not very full and you decide to go down for some more. )

In your scenario, what if you went down with the boom (and the bucket)? This could pick up the back of the tractor and place lots of force on the extended rod.

Volnavy · Apr 24, 2005

OK, make it three cylinders. I will talk to Kubota tomorrow and then share what is going on. THis makes five weekend without the operabiity of my 24,000$ purchase. This puts my construction way behind schedule. I think they need to fix the tractor and compensate me for my losses.

Henro · Apr 24, 2005

OK, make it three cylinders. 

/forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif

Holly heck! Did you have the camera running like you intended?

What a bummer...

Like I think I said in a previous post...I have never hesitated to push or pull with my BL4690 over the last couple years...never a hit of a problem. I don't abuse it with trying to lift the tractor or do side pushes with the boom...but I don't fear stalling it when trying to break a root or pull/push on a stump.

Did you see the post where someone just posted a pic of a BH90 hoe with a bent cylinder?

Mabye there is a supplier problem at Kubota, and defective cylinders being provided with the newer model BH75 and BH90 these days?

If it was a failure during normal operation, be sure to stick to your guns and get it resolved the way it should be!

Good luck and sorry to hear about the third failure!

powershop · Apr 24, 2005

All I can say is my friend had the same problem on a older kubota unit. After several cylinders they rebuilt the relief valve and no more problems. Dealer said pressure was spiking when it would not release and it would bend the cylinder as there is more travel in the cylinder than movement in the arms. Anyway it fixed it.

Volnavy · Apr 26, 2005

OK, I called them Monday morning at 8:15 for their weekly Monday morning wakeup call, and now it is Tuesday night. I had to call them and they said they were going to replace the cylinder again (3rd time in last three uses) and reset the stops.

I am not happy with this reply, it is the same thing they said last time. I also told them I needed it back this weekend and they still have not picked it up.

Any ideas or phone numbers for the Kubota Lemon hot line? I'm to the point at which tomorrow I'm going to ask them for a weekend loaner or for my money back! I am starting to feel like Ramon...

gduff · Apr 26, 2005

I was about to buy a BH90. (There is another thread about a problem with that model as well) I think I might wait a little to see how these bent cylinder issues end up or to see if it is the start of an epidemic. Either that or maybe go with a woods. Three of them! /forums/images/graemlins/confused.gifThis sure sounds like it could be a design flaw. I hope it works out for you and soon!

ArkCivEngr · Apr 26, 2005

Being a new owner (17 hours) of an L3400DT with a BH75, I've been keeping a very close eye on this thread. Not having seen what you're doing, I can't get any real idea of what sort of action you're putting on your hoe, but I've been digging out stumps by first digging "moats" around them--smaller stumps only require one setup and a 1/2 moat, and then I use the curl cylinder to see if it'll pop out. If not, I switch sides, complete the moat, and then pop it out.

What I've found to be the main problems are cedar and elm stumps. Roots galore! /forums/images/graemlins/tongue.gif The only solution I've found is to keep moving away from the stump until the curl cylinder can break the root; then I move back in and re-start the moat.

In doing it this way so far, I've gotten quick and shifted the rear end around only once or twice. If this is something close to what you've been doing, there are two possibilities: 1. I'm lucky or just working on borrowed time or 2. perhaps your dealer is giving you the wrong type cylinder?

When I went down to pick up my tractor, I took a couple of printouts of the pictures you posted at the top of this thread, and when the salesmann saw them, he scratched his head for a minute. I asked him if he'd heard of any possible defects or recalls on these cylinders and his response was "no, that looks like the results of someone trying to hammer something with the bucket." I am quite certain that you haven't been doing this, but I didn't say anything. I'm still a bit uneasy.

Volnavy · Apr 26, 2005

I have dug out several stupms with mine and never had a problem. The problem occurs when digging a ditch in close (dipper stick fully extended) and curling the bucket. I have a ten second clip of it posted on the internet but have not decided to post the link to the group yet (did not want to burn my bridges). I did forward it to Kubota and they said my digging style was normal and I was not putting the unit under undue stress. They said they need to adjust the stops (heard that last time).

I am getting frustrated now because I asked for a loaner for the weekend and they seem to have ignored my request. The dealer said they forwarded it to Kubota, but I have heard nothing. I think they should have followed up and given me an answer by now. I guess it is going to be my responsibility to follow up on it tomorrow. I also asked for compensation for losing my last five work weekends, no reply on that either.

Stef · Apr 27, 2005

I'm really looking forward to see that clip. I have the same backhoe but didn't use it yet. I must say that I'm very curious and if I can see your clip and do the same thing and if the cylinder bends then it will surely prove something. You can PM me about that.