BH75 Piston broke, twice! Design problem??

[Junkman]

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]

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]

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]

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]

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]

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

 

[Volnavy]

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]

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]

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]

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