Backhoe B21 backhoe bucket - slow/weak curl

[joea99]

I picked up a Kubota B21 with under 900 hours, last fall. Ran it a bit, then it got cold and sat.

When trying it out everything seems to work OK, but the bucket "curl" seems weak. The soil here is quite rocky with bit of clay like dirt holding things together. Mid Hudson NY, Catskill area.

Just seems to "stall", can hear pump still trying, but not going anywhere. Arm seems to pull fine, just the curl seems weak. I swapped to a narrower bucket (12" or so) and it seems to curl a bit better.

Ideas?

 

[dfkrug]

Can you tell by the sound if the hydraulics are going to relief? If not, then you prob
have worn piston seals.

Does the curl force get better when you rev up the engine to max?

 

[joea99]

Can you tell by the sound if the hydraulics are going to relief? If not, then you prob
have worn piston seals.

Does the curl force get better when you rev up the engine to max?

Well, it made a bit of a different sound when stalled, but I don't know if that is the relief lifting.

 

[joea99]

Back to this after getting frustrated digging out tree root ball. The curl seems weak and when it stalls, I do hear a hissing or whistling sound. Not being very experienced with such things, I really have no idea if it is the relief, or leaking past the piston seals.

Is there an easy(ish) way to isolate it, or just pull the cylinder and tear it down? Since I only hear that sound when the bucket stalls on curl, not when anything else stalls, it is safe to assume it is the cylinder?

 

[Smokeydog]

Maybe a gauge with fittings to splice into your curl circuit to measure? Could then measure other circuits to compare. Might just be as easy as adjusting the curl circuit relief. It probably sees more deadheading that most.

Since a new to you machine might try doing a full maintenance service with Kubota filters and sudt oil first. While These machines are tough and durable their maintenance diets are picky.

 

[dfkrug]

Is there an easy(ish) way to isolate it, or just pull the cylinder and tear it down? Since I only hear that sound when the bucket stalls on curl, not when anything else stalls, it is safe to assume it is the cylinder?

You can tell if your piston seals are passing oil by operating the curl circuit to relief and placing your hand on the cyl over the piston (in a safe way). You will feel and hear the bypassing. I have used an IR thermometer to detect this kind of internal leak with loader cyls, but you only have one cyl for curl on a hoe.

Don't take apart your cyl until you have more evidence of the problem area. It is true that you could have leaky work-port RVs on the curl circuit, which are not usually adjustable.

 

[joea99]

Maybe a gauge with fittings to splice into your curl circuit to measure? Could then measure other circuits to compare. Might just be as easy as adjusting the curl circuit relief. It probably sees more deadheading that most.

Since a new to you machine might try doing a full maintenance service with Kubota filters and sudt oil first. While These machines are tough and durable their maintenance diets are picky.

One of the first things I did was change the hydraulic fluid and filters. In fact the filters came with the machine.

I was concerned at the time about getting all the old fluid out, was told not be be. However when I redid the seals on the stick cylinder I was dismayed to find some rather nasty looking old oil still in there. Maybe 10 or 20 hours since the change. I'd though that enough to mix it.

 

[joea99]

You can tell if your piston seals are passing oil by operating the curl circuit to relief and placing your hand on the cyl over the piston (in a safe way). You will feel and hear the bypassing. I have used an IR thermometer to detect this kind of internal leak with loader cyls, but you only have one cyl for curl on a hoe.

Don't take apart your cyl until you have more evidence of the problem area. It is true that you could have leaky work-port RVs on the curl circuit, which are not usually adjustable.

I have a dummy question. How can I tell if a circuit has "gone into relief"? Is there a distinct sound? I can make out different sounds, but usually wear hearing protection when operating, so never really paid attention.

Guess I need to get a pressure gauge and some fitting and check a few things.

 

[dfkrug]

I have a dummy question. How can I tell if a circuit has "gone into relief"? Is there a distinct sound? I can make out different sounds, but usually wear hearing protection when operating, so never really paid attention.

Guess I need to get a pressure gauge and some fitting and check a few things.

When you operate a cylinder to the end of its travel, the pump usually goes into relief. The sounds of the pump, engine, and RV itself all change somewhat. If the piston seals leak too much, then the system RV may not operate at all, so the change in sounds you hear will be different.

Operate a known good cylinder to the end of its travel and listen carefully with your ear plugs out.

 

[joea99]

When you operate a cylinder to the end of its travel, the pump usually goes into relief. The sounds of the pump, engine, and RV itself all change somewhat. If the piston seals leak too much, then the system RV may not operate at all, so the change in sounds you hear will be different.

Operate a known good cylinder to the end of its travel and listen carefully with your ear plugs out.

There is a difference in sound when I reach limits on all circuits. That same sound happens when I raise the backhoe boom, but not when lowering, and when raising the bucket. I've always heard that, but took it to be due to increased engine load, but never really noticed any RPM change. I should say this is the first machine I have owned. Used rentals in the past and never took notice as long as they worked.

In answer to someones earlier question, the performance does improve when I raise the engine RPM to 2000 or above. Never took it over 2500.

So I need to break down, look in the WSM and get a pressure gauge and fittings.

 

[joea99]

Well, maybe some operators need to be better trained. Need to talk to his boss . . .

It did seem to be weaker to me than last I used it

I checked, out of the blue, the BH/3Pt selector, seems it was not fully into the BH position. I had recently had the BH off for box blade work, and thought I had set it properly. But, there it is.

It now appears stronger and, while it is not a beast at stump pulling, I did mange to dig out a fair sized white pine, with the last minute or two spend just "rocking" it till it gave up. It did "stall" a few times, but taking a smaller bite seemed to be the ticket there. I presume it is normal to start smelling hot oil when working hard, but started taking it a bit easier, just in case.

So fairly confident now there are no seals leaking as there are no discernible noises or vibrations in the cylinders at limits.

 

[rScotty]

Digging out stumps is about the hardest work for any backhoe. It's hard even on a full sized hoe.