BL4690 Bent cylinders

[kubotaboy348]

Well it is nice that I finally found others that can bend the BL4690 crowd cylinder. And now I know what to avoid. It seems that when things are digging well and you get to a critical point in a trench that is when you will bend that cylinder rod. I just bent my fourth cylinder yesterday, a 12" deep trench crossing a hard packed road. Crowing in while curling the bucket to clear the bottom of the trench.

I bent the first one while digging my first trench from my lake to the house for geothermal lines. That was in soft soil, Kubota said it must have been abuse, so I bought a new cylinder. They are fairly easy to replace, guess I now know what is behind their design. It did not take long to bend the new cylinder, about 15 feet from the house crossing a hard packed drive. Dealer took the hoe back for analysis, and finally said he replaced the valve assembly due to a sticky pressure relief valve.

All seemed to work well after that for a year of so, then out of the blue while digging a trench for a knee wall by the house I executed the now known maneuver for bending crowd cylinders. That was about 3 years ago, since then I have dug lots of different areas with out incident. Doing that
same crowd while curling. Seems that the key is the hard bottom where the bucket can cause the greater torque while curling and force the dipper arm back on the crowd cylinder.

New cylinder from Kubota Georgia plant goes for $373. My guess is they get cheaper the more they have to replace them.

 

[leonz]

Another good case to install a cylinder stop tube to reduce or eliminate damage to cylinders.


Did you have the bucket level or near vertical? that is critical as the circuits do not have

individual relief valves.


The "Crowd" term in excavating is actually the forward motion of a dipper bucket excavator

system but the damage is still the same.

 

[_RaT_]

No one should have to protect the design of this hoe with supplements. I think anyone considering the purchase of this model hoe should read this post. I know I for one would not purchase it. That's ridiculous. Its not operator abuse, its BAD engineering. Sorry for all your trouble, I don't know how you can continue to rely on this hoe, I'd always be concerned.

Another good case to install a cylinder stop tube to reduce or eliminate damage to cylinders.

 

[dfkrug]

Its not operator abuse, its BAD engineering.

....or bad manufacturing.

I think that these hoes have a slight mis-alignment of the boom/dipper pivot
or the upper dipper cylinder pivot.

Is there a consistent direction that the rods bend, left or right? That's
a clue. If it always bends in line with the boom, then it is still a mystery.

Some hoes have significant clearance between the dipper and boom at
their shared pivot. Kubota shims this clearance with the B21 hoe. I don't
know what they do with the 4690. I have added shims for my hoes.

 

[leonz]

The issue is one of a bad cylinder more than anything where a stop tube would have prevented the amount of damage to a greater degree.

I am almost postive the the piston created a gouge/slash in the barrel when it was retracted due to the flexing of the rod damaging the packing gland and stuffing box of the cylinder and the piston became wedged when the dipper arm was extended and the cylinder barrel became egg shaped and no longer useable.


The ONLY way that dipper arm will continue to work properly is to install a shorter dipper arm cylinder with a stop tube that is sized properly for the desired stroke as the cylinder is tooo d*** long period which is WHY IT BENT!

The stroke will be maintained, the cylinder will be located closer to the pivot point, and a stop tube sized for the stroke will limit the fully extended length which will reduce any chance of damaging to near zero.




The little pyramid welded into the dipper arm is a way to cheat and gain more reach in the trench thats all its good for, and as there are no circuit reliefs its going to happen again............

You cannot overcome physics and the mechanics of resistance, action and reaction to linear movement in compacted soils if the mouse you bring to the game is too small to smack the cat.

Thses things are buit for the market they serve and they throw engineering and common sence out the window along with the baby and the bath water.

If they had a Z bar linkage installed it would not have happened but thats an issue dealing with patents and licensing from other machinery builders.



leon

 

[newbury]

I've a Woods BH70-X, has anyone heard stories of this happening on them?

 

[Jay4200]

I've a Woods BH70-X, has anyone heard stories of this happening on them?

No - this seems a common problem on Kubota BHs though. I've read many incidents of cylinder damage on them. Definitely a serious design flaw, which might propagate throughout their line. Don't know.

Woods makes good backhoes. I have a Woods 9000 BH, and I beat it mercilessly every time I use it. It was well used when I got it, and I've been abusing it for 5 years (so far) with flawless performance.

JayC

 

[_RaT_]

Again, in my opinion something that should have been addressed in the design. I'm not even sure what a stop tube is. If you are trying to limit the stroke on a hydraulic cylinder, why not either call for a shorter stroke or design the pivot point to accommodate the length. Either way, its should all be on Kubota's dime for repair and a fix to what appears to be an ongoing issue. .

The issue is one of a bad cylinder more than anything where a stop tube would have prevented the amount of damage to a greater degree.

I am almost postive the the piston created a gouge/slash in the barrel when it was retracted due to the flexing of the rod damaging the packing gland and stuffing box of the cylinder and the piston became wedged when the dipper arm was extended and the cylinder barrel became egg shaped and no longer useable.


The ONLY way that dipper arm will continue to work properly is to install a shorter dipper arm cylinder with a stop tube that is sized properly for the desired stroke as the cylinder is tooo d*** long period which is WHY IT BENT!

The stroke will be maintained, the cylinder will be located closer to the pivot point, and a stop tube sized for the stroke will limit the fully extended length which will reduce any chance of damaging to near zero.




The little pyramid welded into the dipper arm is a way to cheat and gain more reach in the trench thats all its good for, and as there are no circuit reliefs its going to happen again............

You cannot overcome physics and the mechanics of resistance, action and reaction to linear movement in compacted soils if the mouse you bring to the game is too small to smack the cat.

Thses things are buit for the market they serve and they throw engineering and common sence out the window along with the baby and the bath water.

If they had a Z bar linkage installed it would not have happened but thats an issue dealing with patents and licensing from other machinery builders.



leon

 

[kubotaboy348]

The bucket was level, clearing the bottom of the 16" deep trench. Front of bucket hit a hard pack something while crowding, I was not at full crowd when the cylinder bent. All 4 of the bends have been straight in-line and down as shown in initial post. Finished digging the trench with the new cylinder, but I maintained the boom distance to prevent the close crowd.

Yes, I have no confidence in this backhoe, will be looking to replace it with a good WOODS hoe.

 

[rswyan]

I have the same model hoe (purchased new) mounted on our B2910 ...... I have quite a few hours on it (probably several hundred), including digging out over 100 tree stumps (easily) ..... I have not babied it .....

I have not experienced similar problems (knock on wood) - in fact, other than a leaking fitting on one of the stabilizers, the hoe has been problem-free .....