CAT hydro cylinder fail after a very short time......?

[Nige]

I will ask if I can be part of the tear down but i'm sure that won't work out. They are busy and prob don't need me eyeing their work......For all I know, it was something we did!

I dunno. You are the customer. If something failed such a short time after being installed IMO you have every right to ask to be present when it is disassembled. And if it was something you did when installing the piston/rod assembly then again it might be a good idea to be there when it is pulled apart so that you can see the damage for yourself. My 2c, YMMV.

 

[fastline]

I dunno. You are the customer. If something failed such a short time after being installed IMO you have every right to ask to be present when it is disassembled. And if it was something you did when installing the piston/rod assembly then again it might be a good idea to be there when it is pulled apart so that you can see the damage for yourself. My 2c, YMMV.

I agree! But I have also been on the other side of the stick. I use to do some forensic work on race engines.

But having seen how companies work on cylinders, this is why I want to do my own. They move fast. I tend to think debris from the old seals was in the head, but that is purely a WAG! As long as there is no serious damage, hopefully we can just proceed.

The cylinder appeared leak free for the first 10hrs or so, then developed just a tiny weep. Just enough to make you mad but not even enough to run down the cylinder. I would think a blatant error would have shown up instantly.

I inspected the rod and requested they do the same and we both agreed it was good to go. I have found the smallest of imperfections but nothing you can really hang a finger nail in.

 

[Nige]

I inspected the rod and requested they do the same and we both agreed it was good to go. I have found the smallest of imperfections but nothing you can really hang a finger nail in.

Was the rod checked for straightness.?

 

[Welder Dave]

I don't think most shops would want customers in the shop when they are actually working on something due to liability. Even if they aren't actually working on your piece, they could be working on other customers pieces in near proximity. What is common though is for a shop to bring you in the back after they've done the work and discovered the issue or didn't find an issue. I've seen that before to where there didn't appear to be anything done wrong. I was brought in the shop after they took my rotary cylinder apart. They showed me that the shaft had worn a groove in it from the seal. I'm thinking that's gotta be an expensive shaft. Thankfully they said it can be metalized (spray welded) with a harder steel and be machined back to size. I didn't need to see them take it apart. Most people wouldn't want a customer looking over their shoulder or getting in the way when they're trying to work. I can just see some customers trying to tell the shop how to do it or constantly asking questions. There are many good reasons for not letting customers in the shop when they are actually working on your stuff. Sometimes there are exceptions but not often. As far as a cylinder bench there are several you can look up on the internet.

 

[Welder Dave]

Was everything well lubricated when putting the cylinder back together and have there been any other issues with the hyd's. prior to this cylinder leaking? Also when was the hyd. filter last cleaned? It's not as critical on cylinders that the oil is clean enough but if there was even a slight bit of contamination in the circuit for this cylinder could cause a leak in short order.

 

[funwithfuel]

Cylinder was cycled several times very slow, without rod end connected to boom. Cylinder was moved horizontally with ports up to encourage all air to leave.

I did notice the cylinder seemed to be a bit 'tight' in that it seemed to labor the engine a touch and need more stick. This was without eye connected. I suspect that was just the new piston seal as those are stupid tight. The head otherwise moved just fine. No odd behavior during assembly.

Not to be picky, you didn't run to "end of travel " until you were confident all the air was out? Right? Some here will disagree, others agree. Foamed or areated oil will diesel in a cylinder much quicker than any would believe. In my younger life, ruined a set of seals by being impatient. Lasted maybe 2-3 hours. In my defense, it was a dipper cylinder on a 700, so ... kinda hard to push air downhill.

 

[fastline]

I am willing to take a good keyboard lashing in the sake of learning something here. Not a rookie here, but hydros are my least fav. Electrics are my jam.

Machine has good hydro filters, CAT oil only, clean system, never a failure, no other cylinders leak, I try to keep this one "high and tight". The other boom cylinder is perfectly happy. There is nothing that leads me down the road of a system problem, but could point to something in the cylinder. Nige asked about straightness of the rod. No, we did not check that because I have never had a bent rod. Something to consider though. I am usually quite good at examining for failure modes ,thus why I wanted my old seals back. If they had looked mostly good, I might have had concern, but they had the obvious signs of being "timed out".

As for how we purged, I personally feel we are extra cautious here. Cylinder was taken from stop to stop several times at about 20sec per stroke. Everything was hosed down with oil during assembly. We adjusted cylinder position to ensure air would leave (high point) sort of thing. Probably cycled the cylinder 20x, then connected and ran some slow testing.

Everyone knows how the boom cylinders position in an X so head end really should stay purge without much issue. But I guess if there is air in the lower piston side, that really has no way to purge. However, air molecules are way smaller than oil so I always figure air will find it's way past that piston and make it to the head.

I will say, before the repairs, that boom would stay up for days. After the repair, I didn't really test extremes but would set the bucket 1ft off the ground and it would be down the next day. I realize that points to the piston seal and they installed it on the piston and I put in the barrel. I asked that the piston be wrapped and they did that. I didn't see anything on the seal of concern. It was just a super bitch to get in!

Basically in any sort of rework like this, I like to try to find that "smoking gun" to ensure we have it fixed. Go slower on air purge, precharge the cylinder, I have not decided yet.

 

[funwithfuel]

The condition of the packing and head seals will tell you everything. I'm not trying to knock your work by any means. I'm just sharing my personal experiences to help prevent a repeat failure, if it was a contributing factor. Even when I have a hose failure, I exercise the circuit from the middle to maybe ¾ of travel in each direction slowly and deliberately as you described but going a little further each time closer to "end of stroke " each time. As you stated, it should have purged with ports on top. The air should have worked back to tank.

 

[kshansen]

Not to be picky, you didn't run to "end of travel " until you were confident all the air was out? Right? Some here will disagree, others agree. Foamed or areated oil will diesel in a cylinder much quicker than any would believe. In my younger life, ruined a set of seals by being impatient. Lasted maybe 2-3 hours. In my defense, it was a dipper cylinder on a 700, so ... kinda hard to push air downhill.

Wish I still had access to service info from Cat. I recall there was a warning about how to purge air from, I believe it was, the big long tilt cylinder for the bucket of the 988H. Seems it was just that some kind of warning about "dieseling" if not done proper.

Maybe someone out there has access to that info? Nige?

That was the only place I remember seeing anything to do with that in all the service manuals I worked with over the 45 years I worked on all kinds of machines with hydraulic cylinders. Then again the 988H does have a long tilt cylinder where compared to say a 988 87A!

 

[funwithfuel]

Nige has posted that info on here before. I'm usually reluctant to bring it up because it usually starts an argument with "those that know better" But if a guy has a problem with a fresh install, I figure, can't hurt.

 

[fastline]

I should clarify that we never just go end to end, we move back and forth and sort of 'work up to it'. In all ways, I feel we did a reasonably prudent precycle. I know some guys that will throw a cylinder on and go to work. And they never have problems.....lol My life.....

 

[fastline]

Just an update, I am losing confidence in this hydro shop. I felt like I removed some pressure to expedite the repair, I just wanted it right. Almost 2 weeks later, I still had heard nothing so I called to hear they are "waiting on a part that should be in tomorrow".... But what concerns me more is she said "a part that goes under the piston seal was missing"... First of all, the piston was not even the primary issue, though I did note that it would bleed down, which it never did before. Still within CAT specs, but very obviously went backwards somewhere.

I reinforced the fact that the HEAD was the primary issue and I want to know what happened. I think what did not really surprised me is parts were missed in the rebuild. what I personally suspect is the critical Oring between piston and rod. Or the entire energizer band? I mean, WTF? I guess I am just venting as I need to explore building a hydro bench. People make mistakes yes, but I very much question the competence in that shop. Like everyone, I don't think they can find help beyond burger flippers.

Frustrated.....

 

[Welder Dave]

Maybe wait and see what they say was wrong and what part was missed/missing. Bleeding down is likely due to piston seals. If a seal was missed between the rod and piston could cause it. Some pistons are 2 piece with an o-ring in-between them. If that o-ring is missing would cause a slow leak down.

 

[fastline]

Maybe wait and see what they say was wrong and what part was missed/missing. Bleeding down is likely due to piston seals. If a seal was missed between the rod and piston could cause it. Some pistons are 2 piece with an o-ring in-between them. If that o-ring is missing would cause a slow leak down.

Again Dave, the primary reason for removal was the head was puking oil everywhere, and the wiper was half out. their response is "we missed a piston seal, we will get that fixed for ya"....

I think my judgement decided I need to make an unannounced visit tomorrow to see this, in hopes before they try to assemble it. My gut is telling me they are trying to cover something up or they didn't give this cylinder 10min of consideration.

 

[Welder Dave]

You said the cylinder would bleed down and it never did before. That indicates a problem with the piston seals. Maybe they missed something putting it back together. Hopefully the 2nd time they get it right. As far as it leaking at the gland nut, a wiper seal doesn't hold any pressure. It just prevents dirt getting pulled into the cylinder. I would think they'd be extra careful making sure everything is right since they have to take it apart again.

 

[fastline]

I didn't imply that the wiper was holding anything other than I've also never had one walk out. As I have learned though, as soon as the wiper failed, the head seal will fail and probably chew on the rod too. I have no idea what went wrong but I DO know that any piston seal issue did not cause the head to leak.

I guess I just don't share the camp of "try again, see what happens". I've been building engines for 30yrs, and machinist for 20yrs, and that mentality gives me nightmares.

I do know I recently did the tilt cylinders on my forklift and was beyond pissed that I realized the lip on the piston side of the rod was sure to screw up the head seals so we had to remove the clevis on the other end. Even made a tool for it. I realize shid happens but they should have way more tools than me. Even I knew I could just turn an install tool in our shop for that. I wondered on that job how many would just force it and go.

 

[HarleyHappy]

Again Dave, the primary reason for removal was the head was puking oil everywhere, and the wiper was half out. their response is "we missed a piston seal, we will get that fixed for ya"....

I think my judgement decided I need to make an unannounced visit tomorrow to see this, in hopes before they try to assemble it. My gut is telling me they are trying to cover something up or they didn't give this cylinder 10min of consideration.

They are going to bullcrap you, I’m sure you are already expecting this.
Stay calm, get used to being disappointed for expensive work for the future.
Rebuliding a hydraulic cylinder isn’t on a phone app.
Its really nothing the shop will be able to do about it in the future.

 

[IceHole]

Not sure why this went any further than a phone call to xyz shop.

Hey shop, that cylinder I had rebuilt is leaking, I'm dropping it off tomorrow.

 

[Zewnten]

First, if you were talking to the receptionist and not the service manager or tech you should take every diagnostic provided with a grain of salt, they’re there to make appointments and collect money. It very well could be missing a part on the guide nut allowing the hydraulic oil on the rod side to leak past and she misspoke.

Second everyone on this earth was at some point and time was barely “help beyond burger flippers” yourself included so yeah the people might need training and unfortunately you were the client that got caught up in it. Your choices are either let them make you whole or cut your losses.

I get that it’s frustrating to be kept in the dark with no communication but it’s the holiday season and your expectations should match or you’re setting yourself up for disappointment, that’s all on you.

Third parts are taking forever to get anywhere right now. So let’s say they tore down the cylinder on a Tuesday, and wanted order parts. Did they ask if you wanted expedited shipping? If you said no there’s a week or more on that if their supplier had it on the shelf. Add in the holidays and yeah 2 weeks before a part comes in.

 

[Welder Dave]

Not worth getting so stressed about it. There's not anybody on this forum that hasn't gave themselves a little shot to the head because they missed some little detail repairing something and they had to take it apart and do it over. Sometimes the minorist little detail is all it takes. In the case of a cylinder it could be as simple as forgetting or not using enough oil the internal (gland nut) seals when putting the cylinder back together. Guessing the proper torque on the piston nut could be another example. Not quite tight enough and it could come loose. Mistakes can happen that weren't intentional.