JCB Backhoe Valve Sticking Badly

[Piston]

I have a bit of a brain teaser.

I recently bought a 1994 JCB 217S, in non working condition. I bought it not running, but ultimately got it running and was able to lift the backhoe up to engage the locking pin and keep it in the raised position, then brought it home.


When I bought it, the dipperstick function was 'frozen' in a position other than the neutral position. I removed the spool from the backhoe valve block for the dipperstick. It was a bear to get out, and I ended up "gently forcing" it out with a rubber mallet. I did not see any metal pieces fall out, but my assumption was there was a piece of metal stuck in it.

I reinstalled it, however it wouldn't go in very easy. It is too 'tight' to use. If I were to function the dipperstick it would freeze up/get stuck and I wouldn't be able to use it. I was able to gently raise the boom up off the ground so I could transport it down the road to my house.

At this point it is nothing more than a front end loader.


However, here is the brain teaser. My neighbor had this problem in the past, which seemed to stem from a retired elderly mechanic that worked on the machine and 'forgot' to put the hydraulic filter back in place. After it froze up the first time she had another mechanic come fix it. He replaced the entire valve block assembly for the backhoe with a used one from JCB. After installing it, and replacing the hydraulic filter, and changing the fluids, it was supposedly working just fine, as normal. Then at some point it froze up again and here we are.
I have the old valve block as well.

I took it apart and found this chunk of metal in the dipperstick spool.


After removing that piece of metal, the spool still will not go back into the valve block very easy. I removed the other two spools on either side of the bad one, and they came out like butter. I tried for the heck of it, to put one of those spools into the dipperstick section of the valve block, and it also would NOT go it. It is strange, both backhoe valve block assemblies have the exact same problem at the exact same spool?

Does anyone have any tips or info that could help me out? I can't figure out how to fix this.

 

[Tommy Bondo]

I've been blessed over the last 30 years and haven't had a lot of encounters with the JCB stuff but I have a doosy of a story about a JCB hoe that experienced a similar same fate.
Seems this rich guy bought a piece of property in a ritzy part of the county and bought a used JCB hoe to do a lot of the work himself. Rockville CA to be exact and there's a reason they call it that. Anyway, this guy gets this thing stuck in a bad spot with the crowd and swing left stuck tighter than bugs t**t and calls us to come out and see whats up. Remember this was years ago before the week or more waiting list to get a tech out on site became the norm. So I show up a day or two later and this guys been running this thing for hours trying to get it to move and its hotter than a two dollar pistol and leaking oil from everywhere except the tires. The first thing that came to mind was the evil despicable things I could do to my service manager but then the rich guy started mansplaining things to me. Had to make sure we were on the same page and assure me he was a pro I suppose. Anyway the story gets even better after that.

 

[Piston]

I've been blessed over the last 30 years and haven't had a lot of encounters with the JCB stuff but I have a doosy of a story about a JCB hoe that experienced a similar same fate.
Seems this rich guy bought a piece of property in a ritzy part of the county and bought a used JCB hoe to do a lot of the work himself. Rockville CA to be exact and there's a reason they call it that. Anyway, this guy gets this thing stuck in a bad spot with the crowd and swing left stuck tighter than bugs t**t and calls us to come out and see whats up. Remember this was years ago before the week or more waiting list to get a tech out on site became the norm. So I show up a day or two later and this guys been running this thing for hours trying to get it to move and its hotter than a two dollar pistol and leaking oil from everywhere except the tires. The first thing that came to mind was the evil despicable things I could do to my service manager but then the rich guy started mansplaining things to me. Had to make sure we were on the same page and assure me he was a pro I suppose. Anyway the story gets even better after that.

What did it end up being?

 

[Tinkerer]

What you described suggests that the problem spool is the wrong one for that section of the control valve.
The bore in the control valve section has to be in pristine condition.
Unfortunately spools cannot be purchased separately.
The entire section has to be replaced.
All of the "O" rings between the sections should be replaced if you do in fact replace that section.

 

[stinky64]

Don't know if it'll help your condition, but one of the swing functions on my case hoe was stiff as hell probably caused by moisture in the entire system from a total lack of maintenance and sitting in a field for years, I used a 5/8 ball type hone ever so lightly cleaned inside of valve body and haven't had a problem since, give it a whirl, lots cheaper than the alternative.

 

[Tinkerer]

stinky; what did the bore look like before you honed it ?
I have never honed one. Too much of a risk to oversize it for me.
I have replaced spools by salvaging one from another valve body.
Doing that diminished the leak-down but didn't eliminate it.

 

[stinky64]

The bore for that particular spool was visibly rusted but the spool itself was almost unscathed, cleaned it with a scotch brite pad. I was apprehensive about oversizing at first but figured I really had nothing to lose but the cost of the hone which I have used many times since, win/win. Also worthy of note is I had the entire control valve assy removed for a rebuild due to leaks throughout so it was easy to put that section in a vise and do a delicate cleaning with the hone..Also luckily it was the swing functoin so I really don't notice any leakdown.

 

[Tommy Bondo]

Lots of chewed up metal. Maybe part of the filter that took a trip through the work pump? Or at least judging by the noise this machine was making and some ground up cast steel that was my first guess. I was able to clear the spools and although they were junked I was able to get the boom stowed for the guy. After that I called the boss and we punted it off to the JCB dealership up in Sacramento. We were the local CNH dealership but would work on just about anything within reason. That one was going to be a lot of parts and man hours and didn't need another hangar queen in the shop at the moment. Seeing that valve stack is right there in line after the pump that's not where you want to see any metal because now its most likely throughout the system before it gets back to tank. Bad juju. However that's a rare occurrence and in your case most likely just a piece of casting left over from machining that dislodged and got stuck in the spool. I've seen that kind of thing a few times over the years. So long as you just knock the burr down enough that the spool travels tight and unrestricted in the bore you should be OK. Got a gouge running down the spool or the bore then it's junked though.

 

[Tinkerer]

Piston; If you haven't changed the hyd. filter and cleaned the suction screen, it should be top priority.

 

[Delmer]

Yes, change the filter, and check the old one for debris. Videos on youtube to show how. Post pics of what you find in the filter. Take several samples of the paper.

If nothing horrible turns up, you have nothing to lose by honing it, or lapping it with just the oil in it, or lapping it with fine lapping compound.

We're assuming it's corroded, or scored from debris. But it could also be tight because the spool is bent, or the valve body is distorted from uneven pressure, or cracked.

Does the spool rotate in the valve body by hand? Rig a hand crank to spin it to see if it will loosen up.

 

[stinky64]

I actually encountered a bent spool once on a feed truck control bank,the powers that be sent a new guy out once with not enough knowledge about unloading and run speed or pressures, "poor feller" managed to take out $1200 hyd. pump both circuits and got the hyd. lines so hot that the heavy plastic wrap around loom was melted and dripping off all the hoses involved, lucky that he didn't blow a line to the control box where he was standing, it would have melted the skin off his entire body..

 

[Piston]

Thank you all for the replies so far!

At this point, I've drained the hydraulic fluid and will be filtering all of it through a 7.5 micron external filter/pump. I can see the hydraulic fluid is obviously brand new and very little use on it. I cleaned out the tank using paper towels and magnets.
The tank DID have a fair bit of sludge as well as a "more than comfortable" amount of metal fragments. The strainer looks terrible.


There are obviously a lot of pieces of metal in the system. I'm not sure if they are new, or old pieces, I suppose that is hard to say. When I took the side cover inspection plate off the hydraulic tank, all the paint was still on the bolts, indicating it has likely never been off, so I don't think either of the mechanics did a very thorough job.

It is likely that there were a lot of pieces of metal, as well as sludge, in the tank for a long time, for some reason??? And then when they ran it with no filter in place all of those metal fragments made their way through the system. God only knows how many are in there.

A couple questions come to mind:
Why would the exact same spool, on two different valve blocks, have the exact same symptoms? Is it possible that the one cylinder related to that spool (dipperstick) has an abnormal amount of foreign debris in it, and each time that cylinder is operated it's damaging the spool??? Do cylinder seals have metal parts, or all non metallic?

What you described suggests that the problem spool is the wrong one for that section of the control valve.
The bore in the control valve section has to be in pristine condition.
Unfortunately spools cannot be purchased separately.
The entire section has to be replaced.
All of the "O" rings between the sections should be replaced if you do in fact replace that section.

Unfortunately, these are not individual spool sections bolted together, so my only option to replace the bad spool, is to purchase a 3rd entire backhoe valve assembly, which may be necessary anyways.

Don't know if it'll help your condition, but one of the swing functions on my case hoe was stiff as hell probably caused by moisture in the entire system from a total lack of maintenance and sitting in a field for years, I used a 5/8 ball type hone ever so lightly cleaned inside of valve body and haven't had a problem since, give it a whirl, lots cheaper than the alternative.

I would certainly be open to trying this. Where do you get a 'ball type hone'? Do I measure the exact diameter of the spool and then order the same hone? Does this go on a drill? On the old valve block I did put a borescope camera up into the spool, and it appears (it's hard to tell even with camera) that the bore could have some slight damage on some areas. I have NOT put the camera up into the new valve block yet.

Yes, change the filter, and check the old one for debris. Videos on youtube to show how. Post pics of what you find in the filter. Take several samples of the paper.

If nothing horrible turns up, you have nothing to lose by honing it, or lapping it with just the oil in it, or lapping it with fine lapping compound.

We're assuming it's corroded, or scored from debris. But it could also be tight because the spool is bent, or the valve body is distorted from uneven pressure, or cracked.

Does the spool rotate in the valve body by hand? Rig a hand crank to spin it to see if it will loosen up.

The spool will rotate in the valve body but not very easy by hand. I did rotate it a good 10 turns or so and then pulled it out, to see if there was any scoring on the spool itself. I did not see anything obvious.

At first I thought that maybe the valve body was overtightened to it's mounting plate and possible torqued causing distortion. However I loosened up a couple of the mounting bolts and it made no difference. Then I looked at the old valve body and it seems pretty darned beefy, I can't even imagine it distorting anyways.

I'm really at a loss. My brain thinks logically and I have to understand the "why" behind things, and I can NOT think of anything that would cause the same failure on the same spool in the same spot, on two completely different valve and spool assemblies. I keep coming back to a common failure of the dipperstick cylinder, but the metal parts appear that they come from the gears on the hydraulic pump. But still, even if the metal parts came from the pump, how on earth do they get stuck in the same spot, on the same spool, in the same section but on two totally different valve assemblies?

 

[Delmer]

I was expecting a paper filter, is there any paper filter in the system? rinse that screen off with a solvent and put those particles on white paper with a pencil or something for scale. Doesn't look half bad from here, but it's the iron that counts.

the obvious answer for why the same valve gives trouble is because that cylinder is coming apart.

 

[Tinkerer]

Filtering the tank contents is step in the right direction.
But, a complete system flush needs to be done as soon as the oil from the tank is filtered. It is long, slow process that requires removing hoses from cylinders and extending and retracting those cylinders.
Same spool and two different valve body's --- Indicates a problem with the cylinder associated with that spool.
It definitely needs to be to be taken apart and inspected.
A loose piston may be the problem.
If the cylinder is in good condition, removal and a through inspection of the hydraulic pump seems to me to be next.
If a spool from the original valve assembly fits and moves freely why not use one of them ?
Do you have or need the service manual for your JCB ?
From the service manual ----------

 

[Piston]

I was expecting a paper filter, is there any paper filter in the system? rinse that screen off with a solvent and put those particles on white paper with a pencil or something for scale. Doesn't look half bad from here, but it's the iron that counts.

the obvious answer for why the same valve gives trouble is because that cylinder is coming apart.

It does also have a paper filter, which was just recently changed and looks literally brand new. I don't think they ran the backhoe for an hour after the full service last time.
When you say the cylinder is coming apart, do you mean the seals etc inside the cylinder and on the cylinder rod? Or do you mean the actual rod in the cylinder? Does that happen?

Filtering the tank contents is step in the right direction.
But, a complete system flush needs to be done as soon as the oil from the tank is filtered. It is long, slow process that requires removing hoses from cylinders and extending and retracting those cylinders.
Same spool and two different valve body's --- Indicates a problem with the cylinder associated with that spool.
It definitely needs to be to be taken apart and inspected.
A loose piston may be the problem.
If the cylinder is in good condition, removal and a through inspection of the hydraulic pump seems to me to be next.
If a spool from the original valve assembly fits and moves freely why not use one of them ?
Do you have or need the service manual for your JCB ?
From the service manual ----------
View attachment 264470

I will move to the cylinder next, I'll see if I can get it apart and replace the seals. I have a JCB dealer 20 miles from me and I hope they have the seal kit in stock.
I did try using a spool from a different (working) location in the new spool, but it was still tight. I did not try using the same spool from the old valve, in the new valve. I will try that, hopefully tomorrow, and see if it fits any different.
Monday I should be able to get new filters and seal kit from the dealer, and if time allows, tear into it. I'll take some more photos as well.
I do have one of the JCB manuals that are floating around the internet. It's not searchable however, so if you have one that is searchable that would be very helpful. Without going out and checking, I believe the first 3 of my serial number are 417 but I could confirm that.

 

[Delmer]

Like tinkerer said, a loose piston will shed metal. The nut or bolt comes loose and the piston works against the rod. Or the piston wear ring is gone and the piston is wearing against the cylinder bore, or the cylinder is dented somewhere and wearing against one spot on the piston. Even the gland can wear out and the rod will wear into it.

In this case, I'd take it apart and worry about the seal kit later. Lots of places to get seals.

 

[Tinkerer]

You are doing everything right so far. IMHO.
You could roll the spools on a piece of flat glass to check them for warpage.
It wouldn't surprise me if they are both warped.

I have tried several different brands of programs to work with .pdf files.
I ended up using Adobe Acrobat DC Pro to view and edit .pdf files.
It has a search function that I rarely use. The index in the .pdf documents is all I ever needed to find what I was looking for.

 

[Piston]

Like tinkerer said, a loose piston will shed metal. The nut or bolt comes loose and the piston works against the rod. Or the piston wear ring is gone and the piston is wearing against the cylinder bore, or the cylinder is dented somewhere and wearing against one spot on the piston. Even the gland can wear out and the rod will wear into it.

In this case, I'd take it apart and worry about the seal kit later. Lots of places to get seals.

Thank you, I’ll take the cylinder apart, assess, and post up what I find.

 

[Piston]

I got the cylinder apart. Found my problem! Thanks for the help guys.

First off, I was having a heck of a time breaking the end nut loose. I didn't have a big enough wrench, so I went to Harbor Freight for a $28 36" pipe wrench. I could NOT break it free, even with my "cheater" bar, the wrench kept popping off. Then I found a thread on here about hitting the end of the cylinder where the threads are with a large hammer. I whacked it pretty good, and sure enough, another run with the 'cheater' and it came out relatively easy.
It's now apparent to me that a piece of metal must have gotten sucked into the cylinder when they ran the machine with no filter, and then it likely made a small gouge in the barrel wall, then just kept getting continuously worse with ever function of the dipperstick. The old operator didn't know enough to stop when he felt resistance on that spool, so he forced it over and over, causing damage to the backhoe valve block, then the mechanic replaced the valve block without ever finding the root cause, then the same thing happened again.

I'm glad I found the problem but I'm sure it's not going to be a cheap fix. I believe the ram itself should be okay, but the barrel I can't imagine they can do anything to fix that???

My plan now is to plug the two hydraulic lines to that cylinder and then continue flushing the hydraulic system. After that, I'll work on getting the backhoe valve either repaired/working, or replaced.

Here are a few pics. Notice the dark spots in the pics of inside the barrel, those are very large gouges in the barrel wall.

 

[Piston]

Some more.