Volnavy, you're not alone

   / Volnavy, you're not alone #1  

ArkCivEngr

Silver Member
Joined
Sep 23, 2004
Messages
182
Location
Russellville, Arkansas
Tractor
Kubota L3400DT, John Deere X495
Volnavy, you\'re not alone

I was digging a moat around a particularly nasty Sweet Gum stump last Sunday. This stump was about 2 feet from the edge of my driveway, and some of the roots ran directly under the driveway. That soil was really hard-packed, so I had to clean off the top and under the roots and then cut them with a chain saw to get them out--the bucket curl wasn't near enough to budge them, much less break them out.

After getting the roots out and getting the moat down about 4 feet, I proceeded back to the other side of the stump to "poke" out some dirt between some roots I'd already cut through the day before (this one stump was a 3-day job).

Just as soon as I started pulling the bucket in towards me with the dipperstick: "BAM!" It sounded like a rifle had gone off right beside my head. I knew instantly what happened, and sure enough, the dipperstick piston was slightly bent and snapped completely through.

After looking at it for a few seconds (and fighting the urge to puke), I realized that the only possible way the piston could bend that way was to be put in compression; and the only way to do this would be to push away from the tractor with the dipperstick. Once the piston was bent, digging with it towards the tractor put it back in tension; but since it was bent the axis of the load passed outside the body of the piston and put a fairly large moment on it, which of course it isn't designed for.

The kicker is that I didn't hang up on anything in that trench that I'd dug right before the piston broke. I was VERY careful with this stump (like I said, it took 3 days) and all my motions were exceedingly slow.

Questions:

1. For you others who have popped this piston, did yours break because you'd pushed on something and put that piston in compression? Or do you think that this is more of a fatigue stress issue causing these breaks? My tractor has 42.5 hours on it and exactly 32.5 of them have been hoe work hours.

2. I'm assuming (and praying) that this will be covered under warranty? I read through it the other night and it mentioned that abuse, etc. were not covered. I can't imagine the work I've been doing being called abuse; but just for the sake of argument, if it could be called abuse, why did it take 30 hours of use to break the piston?

3. Volnavy, I seem to recall that your dealer wound up getting you a whole new backhoe. I assume all of your hassle was covered under warranty? And how has the new hoe done for you? I don't expect a new hoe because it took mine so much longer to break than yours; seems like just replacing the cylinder and piston should be enough.

I'll be taking mine back to Fiser on Saturday. Hopefully I won't have to write another post Sunday and vent.
 
   / Volnavy, you're not alone #2  
Re: Volnavy, you\'re not alone

So, do I have this correct?
The dipper cylinder is fully extended... this puts the dipper as close to the boom as it can get.
The bucket curl cylinder is fully retracted... this puts the bucket teeth as far away from the boom as possible.
Lower the boom until the bucket teeth engage a root.
Curl the bucket toward the machine.
If you curl the bucket and lower the boom at the same time then I can see how this would put the most possible compression on the fully extended (and poorly supported) dipper cylinder.
If the right control lever is held inboard while also held to the left then this will keep the oil pressure on the dipper piston while the bucket rotates, or tries to.
But why isn't the relief valve allowing the dipper cylinder to retract and mitigate the buckling stress on the rod?
No offense intended here but I think the position of the hoe could be adjusted to be more appropriate for the use and the control technique may need some improvement but this does not relieve the manufacturer of responsibility. The hoe may be a bit under designed and the relief valving is not working as it should, be that a design issue or mal-adjustment.
According to the recent posts, the manufacturer has been decent when it came to sorting out the broken or bent cylinder issues. I can't remember anyone who had to ante up themselves.
I have a bit of a stump and boulder project for my BH90 in the not too distant future and I will use it to it's full potential and see what happens. I must say I'm somewhat concerned as down time will put more than just me out of work.
I'm far far far from even considering myself an expert so take what I've stated with a grain of salt. I am sorry for your inconvienience and loss of use. Please keep us posted.
Best of luck,
Martin
 
   / Volnavy, you're not alone
  • Thread Starter
#3  
Re: Volnavy, you\'re not alone

As best that I can remember, the bending probably occurred while the boom was at about 45 degrees, but the dipperstick was not fully extended. It's pretty obvious these pistons aren't designed to handle a whole lot of compression, but they should be able to handle more than what I'd put on it. As I stated, I wasn't even attempting to pry roots out; I was simply raking dirt off of them.

I also think that a lot of these bending cylinders will wind up being attributed to fatigue stress due to lower quality metal used in the pistons. Time will tell.

The dealer is going to check the tractor pump and valve settings to see if they're acceptable. Should know something next week.
 
 
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