Harbor Freight backhoe keeps bending cylinders

Maybe not the type of backhoe this sub forum is used to, but Ill ask anyways. Im tired of spending money on this thing.

I had to dig a trench to get power out at my cabin. I dont have a backhoe attachment for my tractor so I borrowed my dads HF ride on trencher.
It has a 9hp engine and you basically drag yourself along while you dig. Its setup to pull behind a truck from place to place.

Anyways, I got most of the trench dug when I bent a cylinder. The trencher itself is about 10 years old and I figured maybe it had gotten damaged some other time and that why it bent. So I bought a new on from HF. They actually have a decent parts inventory for their equipment.
I installed the new cylinder and finished the trench for my power. Backfilled it etc. Then I had to dig a shorter trench for my well water line. I didnt get very far when I bent the new cylinder (same location on the machine as the last one).

So my question is, am I expecting too much from a HF trencher? This particular machine has been used a bit in the past, and hasnt had any issues except for a hyd hose or two needing replacement.

Did I bend something else and thats why the cylinders keep bending? Visually everything looks straight. There is some slop in the pins but its not terrible.

Or am I pushing it too hard? Im digging in rocky soil. Rocks the size of basketballs all the way up to small block Chevy size rocks. All the other digging the machine has done was in Sandy soil.

All my previous backhoe experience is on a 40hp tractor with backhoe attachment. When you hit something it cant move, it just doesnt move it. Thats what Im used to.

Pics are two file photos of the type of machine Im talking about. The arrow points to which cylinder is bending. Last pic is of the first one I bent. The second one I bent isnt as bad, but still needs to be replaced.







Thanks in advance

With the cylinder off and you have it up in the air can you move the boom by hand as in it doesn't bind?? I'd say the relief valve is stuck so you have an over pressure issue because the relief valve should open before the cylinder bends

Checking the pressure is a good start.

Did it bend while using the dipper or did the dipper bend while using the bucket and or boom during a hard lift/pull? It is possible to overload a cylinder during the use of other functions. I don't know how that one is valved/plumbed but port relief valves (separate reliefs in each function's control valve and separate from the main system relief valve) are used on a lot of larger equipment so an over pressure condition caused by another function or condition doesn't cause that type of damage. Rocks the size of small blocks is likely pushing its limits.

This post was edited by Jim.ME on 07/24/2021 at 04:10 am.

So another issue that I thought was unrelated is with the hyd system. If you run the machine for about an hour it will all of the sudden slow way down. To the point that some controls no longer work. Others are very very slow. If you let it sit for a few hours and come back it will act normal again. Ive changed the hyd filter and that has no affect.

It seemed like maybe the original filter, because it had some stringy looking stuff inside that I think was the element coming apart.

The first time I bent it was trying to get a large rock out of the trench. That was the Chevy rock. The second time it seemingly bent for no reason. I was trying to be gentle with it after the first issue. I want to say it bent while using that function, but Im not 100% sure.

The cylinder is off the machine now while I look for a new one. The ones at HF are now on back order. Everything moves freely, and Ive kept the pins well greased.

Ill include a pic of the crap in the filter. So it sounds like maybe I have some contamination in the system thats causing a valve to stick. Or that valve might be bad.

Im assuming the pressure relief valve would be in with the control valves right? What is the big one on the end?

What pressure are you running? It's
possible someone turned up the relief
or it's stuck. Also possible being a
low end piece of equipment that it
doesn't have work port reliefs on the
valve and you are overpowering the
cylinder with the curl function when
it's locked hydraulically. Might be
worth finding a cylinder with a larger
rod to replace it

Honestly Im not sure what the pressure is or what its supposed to be. I need to do some research on that. I dont think someone would have turned up the pressure, but with the issue with it slowing down after about an hour, someone might have tried to fix that by turning up the pressure. Ill talk to the last guy that used it before me.

It could have been set wrong from the
beginning, spend 20 bucks on a gauge
and check. The slowing down could be
oil overheating and especially if it
has some moisture in it. It may not
have a hydraulic cooler since they are
kinda hobby machines for intermittent
use. Adding one may help