JD Hydraulic Cylinder Rebuild Help?

[reasley]

Richard, is it possible that they are not "wrong" but "different"? Have you tried to install them?

There are updates in parts all the time...Maybe you have the latest and greatest.

Good afternoon, Kenny --

As you know from our phone conversation, this was exactly the situation (thanks!) and I now have two of the cylinders rebuilt; a quick lunch break and I'll finish the others.

When I first compared the seal kits yesterday, I was hot (95 here in Central Texas) and frustrated that I was working at maintaining something instead of being productive getting tasks done -- not a good time to work! The first seal that I compared was the main piston seal and the new one was a completely different design -- no taper, about 4X as thick as the old and was in a separate plastic bag within the kit. I quickly concluded (erroneously) that this must be the wrong kit.

After Kenny's suggestion, I systematically put the old sealsand the new seals side-by-side. There were only two differences: the main piston seal (described above) and a flat plastic type seal that was a different color. Then, I inspected another old piston that had not yet been disassembled and realized that this was the failure component that was causing the leak down. I'll post another message later that has pictures to illustrate the failure and the replacement seal and how it overcomes the old seal's weakness.

Again, Kenny, many thanks for helping out this Memorial Day!

Richard

 

[Wayne County Hose]

1. Is there a tolerable level of scoring on the piston? Or, is it a "scored at all, then check the bore, if scored at all, scrap" type thing?

2. I am sure that out of round on these cylinders is not an "eye it" type of thing -- I have a machine shop that can check it for me, if needed. However, going back to Q. 1 -- if there is any scoring evident, is this indicative of either a permanent or momentary bending of the cylinder rod?

Many thanks in advance.

Richard

Hello Richard,

To answer your questions, i will give you more my opinion than anything else. Hydraulic cylinders are a rather mysterious item that there is not much info on, other than stuff written so only engineers understand it. Perhaps if there were someone with a degree in this field, they could answer better than I. Given that, here is my answres to your questions based solely on my experience.

1. Scoring on the piston is an indicator of your second question, rod flex or bent. When the rod flexes, it cocks the piston in the bore. This causes the piston to scrape the cylinder. Unless it is an aluminum piston, the cylinder bore is also scored. The piston is usually okay, the cylinder bore needs to be inspected by someone knowledgable in the field. It can either be honed or needs to be replaced. Cylinder bores need to have a nice even cross hatch pattern to seal correctly.

2. Any machine shop can check the bores for roundness with a simple bore gauge. They measure the bore at at least 2 points opposite each other and compare the readings. very rarely, if ever, have I seen a hydraulic cylinder out of round. They sometimes have dents, or balloon out to the point of almost bursting. Usually any problem like this is very easy to see. But, checking is never a waste of time.

Good luck, Andy.

 

[reasley]

Hello Richard,
1. Scoring on the piston is an indicator of your second question, rod flex or bent. When the rod flexes, it cocks the piston in the bore. This causes the piston to scrape the cylinder. Unless it is an aluminum piston, the cylinder bore is also scored. The piston is usually okay, the cylinder bore needs to be inspected by someone knowledgable in the field. It can either be honed or needs to be replaced. Cylinder bores need to have a nice even cross hatch pattern to seal correctly.
Good luck, Andy.

Good evening, Andy --

Exquisite timing! I had just downloaded some pictures that I was going to post to this thread when I saw your response. Thanks for the insight!

Though I have already assembled all of the cylinders and installed, the pictures do reveal several things. Looking at the originalpistonseal picture, you can see the base O-ring and a thinner tapered seal. The newpistonseal has the same O-ring but a much thicker non-tapered seal. Looking at originalpistonsealmiked and newpistonsealmiked, the difference in thicknesses is significant. Pictures failedseal1, failedseal2 and failedseal3 show how the too-thin original tapered seal is insufficient to do the job, with the failed seal allowing the underlying O-ring to protrude beyond the tapered seal. Upon disassembly, the O-ring had actually separated and disintegrated.

These pictures are close-up enough that you should be able to see the grooves in piston area that I had mentioned in the earlier post that led to my questions to you . . .

Richard

 

[Wayne County Hose]

Richard,

Sorry for the delayed response. I have been extremely busy recently and will be for a while. I have come to dread weekends.

Very good pics. I am very familiar with your piston seal design. It is a very good design but the one I despise working with the most. It is always such a hard time getting the piston seal (yellow ring) over the piston. I guess now you will just have to wait and see how your cylinder behaves. I have seen things put together and thought "No way will that work." But, many times I shake my head in amazement as it turns out just fine. So, I never say never.

I would extend the rod out all the way and check for any bends. Bending usually occurs in the lower third of the rod. The further the rod is out of the cylinder the weaker it is. It's all geometry. Someone like Larry could explain it much better than I. If the rod is bent, you will notice some scuffing in the chrome at the high point of the bend.

The o-ring underneath the piston seal has a different function than you may think. It really doesn't seal anything. It keeps the piston seal "loaded" against the cylinder wall. It just keeps the piston seal in place, keeping the right amount of tension between the piston and cylinder. You obviously have an updated piston seal configuration in your new kit. I've received many new kits with completely different parts and thought that no way that looks right. But, they fit in there and work well. So now I always try the new kit before I panic.

Good job on your cylinders and let us know how it works out.
Andy.

 

[kennyd]

It is a very good design but the one I despise working with the most. It is always such a hard time getting the piston seal (yellow ring) over the piston.

Andy, Have you tried to boil the seals like I suggested above? Makes them go on easier...

How that the JD850 project comming?

 

[Wayne County Hose]

Andy, Have you tried to boil the seals like I suggested above? Makes them go on easier...

How that the JD850 project comming?

Kenny, with this type of piston seal, I place the seal in a bowl of water and nuke it to about 160 degrees. If it really gives me a hard time, I heat the actual piston to about 130 with a propane torch.

The 820 is almost done. I rushed like an idiot to get it done today. Everything was all hooked up and ready to go at quarter to 5. Fired it up, and oil literally everywhere. The old FEL valve has a cracked body and it was gushing like Old Faithful. I'm going to throw on a log splitter valve tomorrow. I ended up rewiring the dash as mice chewed the wiring, installed an exhaust up past the hood instead of under the floorboard, addad 3 lights and a switch, installed the valve with all new hoses, and made a bracket for the bulkhead mounted qd's. Also changed the starter solenoid which had maybe a couple good starts left in it, and changed the motor oil. Oil change was easy, only 1 quart came out.

 

[kennyd]

Kenny, with this type of piston seal, I place the seal in a bowl of water and nuke it to about 160 degrees. If it really gives me a hard time, I heat the actual piston to about 130 with a propane torch.

The 820 is almost done. I rushed like an idiot to get it done today. Everything was all hooked up and ready to go at quarter to 5. Fired it up, and oil literally everywhere. The old FEL valve has a cracked body and it was gushing like Old Faithful. I'm going to throw on a log splitter valve tomorrow. I ended up rewiring the dash as mice chewed the wiring, installed an exhaust up past the hood instead of under the floorboard, addad 3 lights and a switch, installed the valve with all new hoses, and made a bracket for the bulkhead mounted qd's. Also changed the starter solenoid which had maybe a couple good starts left in it, and changed the motor oil. Oil change was easy, only 1 quart came out.

All that as a favor?

At least you know you have the pressure line hooked up correctly! And now you know why it doesn't have a loader on it anymore

 

[Wayne County Hose]

All that as a favor?

At least you know you have the pressure line hooked up correctly! And now you know why it doesn't have a loader on it anymore

Yep, all as a favor. I guess I'm just a nice guy. Well, the tractor owner is a real good guy and I know should I ever need anything, I know they will be there for me.

 

[Hookblock]

Thanks guys for all the info on this topic I to would have been at this project all night, or worse yet given up and taken it to a dealer. The seal kit 25$, the little woman and I figuring it out with your help is priceless

 

[Reg]

I re-built a 5 inch diameter log splitter cylinder WITHOUT the benefit of a snap ring groove filler.
That is to say without one from a kit.
First I pushed the end seal IN a few inches to get some working clearance.
Then I improvised by filling the groove with some of that quick set epoxy body putty, filed it fairly flat once it set.
I left it in while I took the end seal and old piston out, replaced the piston "rings" got the piston back, then the end seal back and pushed in a few extra inches.
Then I chipped it out, which didn't take much because I had left the surface a bit oily so it wouldn't stick too well.
The end seal comes back against the snap ring easily enough, just pull on the rod.