Jinma Backhoe Swing Cylinder Leaking

[Smalljobs]

I'm having a problem with one of the swing cylinders leaking oil. I haven't removed it yet but it squirts momentarily right out the side near the thick midsection where it's mounted. I'm wondering if there's a vent hole there and I seeing oil that made it past the piston seal. I can watch the boom swing and at just one point the oil squirts out and then it stops. I don't recall if it's when the cylinder is extending or retracting. It's hard to see and I don't want to put my head in there with boom swinging.

 

[RonMar]

Mine has vent holes on the swing cylinders. They are about 1/8" in diameter and located about where a front port would be located. I have thought about welding front ports to the cylinders so I can run them in parallel, but I just havn't found the time The problem with the vent hole is it injests dirt and will shorten the seal life. I had an end cap come unscrewed so have had them out, and I found all kinds of crap inside the front end of the cylinder... Adding front ports and crossover lines would close up the front of the cylinder, and add some swing strength to the boom...

Sounds like you have a piston seal leaking

 

[Smalljobs]

Ron - Thanks. I suspected this was the problem. When I imported the BH, I also ordered two extra repair kits for every cylinder!

 

[Bob Rooks]

Mine has vent holes on the swing cylinders. They are about 1/8" in diameter and located about where a front port would be located. I have thought about welding front ports to the cylinders so I can run them in parallel, but I just havn't found the time The problem with the vent hole is it injests dirt and will shorten the seal life. I had an end cap come unscrewed so have had them out, and I found all kinds of crap inside the front end of the cylinder... Adding front ports and crossover lines would close up the front of the cylinder, and add some swing strength to the boom...

Ron,
I think it's more involved than that. I was going to do that with my LW-6 hoe, but it was pointed out to me that I have the wrong type of cylinders to do it. The cylinders must be "balanced", that is, equal displacement on each side of the piston. As it is now, one side has a rod, the other does not. A hydraulic lock will occur in short order. A balanced cylinder wil have a rod sticking out of each end.

 

[RonMar]

How exactly will it bind/lock Bob? I don't see that happening. Right now, the supply lines go to the main chamber/piston ends of the cylinders. These lines connect to the working ports of a single dual-action spool valve, so the two cylinders work just like a dual action cylinder does.

What I am talking about is putting a "T" at the current cylinder attach point on the piston end of each cylinder. From these "T" fittings, I will run lines to the opposite cylinder rod end. IE left rear T'd to right front and right rear T'd to left front. When I give a boom right command, it sends pressure to the rear of the left cylinder to push, and at the same time to the rod end of the right cylinder to cause it to pull. The opposite ends of the cylinders are connected with a low resistance path back to the reservoir. Since the base and rod ends are connected thru a T, the fluid to the different volume cylinder ends will flow as needed thru the two branches of the T. Yes, one cylinder will have more push than the other one will have pull, but because it needs more volume, it will move at a slower rate than the one with less force... I don't see how this can bind as the opposite sides have a free return thru their T and equal but opposite plumbing... the two ends of the opposing cylinders receiving pressure will simply divide the work based on their abilities.

What I do see it doing is adding about 75% more fluid volume required for a given swing, so it should slow the boom down a fair bit(mine is too fast/twitchy now). It will also add approximatly 75% more force to the boom which will be a welcome change as I can hardly push much more than a bucket full of soil off the top of a pile now

 

[EE_Bota]

Using a Tee approach means a parallel connection, and I don't think that is a problem. The piston side will draw more fluid than it's mating rod side, but they are each free to make their own draw (get their own bite at the apple). I think the problem would happen if they were in series.

 

[Smalljobs]

I have the cylinder out and found the threaded gland retainer was finger tight. With the threaded retainer fully withdrawn I cannot seem to pull the rod out of the cylinder. It's almost there but seems to be hung up in the threaded area. Should I reconnect it to the hydraulic hose and use hydraulic pressure (and a bath) to push it out?

 

[Smalljobs]

I finally got the rod and piston out by pulling harder. Now, what's the best way to replace all these parts. I have factory repair kits.

 

[wdchyd]

Clean, polish, clean, deburr, clean, lubricate, clean, carefully reassemble with clean bench and tools, clean and test

 

[wdchyd]

Oh, don't scar the piston head under the seals with pointy sharp tools......:banghead:

 

[Smalljobs]

All set, all seals off. It seems like I should remove the piston head so that I can install the blue lip seal from that end instead of having to force it over all the other grooves?

 

[Smalljobs]

I cannot seem to stretch the blue lip seal over the piston head even after immersing in boiling water. What is the trick to installing a lip seal without the tool?

 

[Bob Rooks]

Does that piston come apart if you remove the nut on the rod? Some do. Another trick, after you have it boiling hot, is to use some steel shim stock around the seal lands. This practice is also sometimes useful when installing the piston into the cylinder. Saves the seal surfaces. A tool that will work well for that purpose is an exhaust tailpipe expander. http://www.harborfreight.com/catalogsearch/result?q=tailpipe expander
It looks like you got the better urethane cup seals too.

 

[Smalljobs]

Bob, Tks. The piston comes apart, but at the other end.

 

[wdchyd]

I cannot seem to stretch the blue lip seal over the piston head even after immersing in boiling water. What is the trick to installing a lip seal without the tool?

Think "Tire Machine".....using slender smooth screwdriver and grease.....work fairly quick, no need for hot water....it'll drop right in with a twist

 

[Smalljobs]

Thanks! I brought the seal and piston head to a local hydraulic shop this morning. He brought the parts into the shop and returned in less than a minute...all done! He would not accept any payment or even a coffee. Now I know where to buy fittings and misc help.

 

[Smalljobs]

It's all back together with no leaks but the other one, #2, is now leaking out the same vent port. It never leaked in the past. When I removed the upper bar that retains the cylinders I noticed the upper stub bearing had lifted up allowing the #2 cylinder to be unsupported on the top. Now that's it's properly restrained, it leaked on every push stroke. Suddenly it stopped. I wonder what's going on here. I really need to use the BH this weekend and will avoid any end of swing where the relief valve hits maximum pressure. Yup, I have a gage on it, and it relieves around 2200 psi. Any ideas what happened to the #2 pistoni lip seal? It's never been repaired and the BH probably has less than 40 hours on it.

 

[Smalljobs]

#2 Still leaks just like #1 did at the outset. The BH was stored outside under a tarp during the winter and I'm wondering if the two vents ingested enough moisture to damage the end of stroke areas. I found a lot of gunk and minor surface corrosion at the unswept area of #1 when I took it apart. It really seems strange that #2 never leaked and now it does. Maybe during the repair of #1, when I swung the hoe over one way and then the other, the piston head of #2 passed over the normally unswept area?

 

[RonMar]

Thats possible, when you had #1 out, the boom could swing past where #1 would have normally stopped the swing allowing #2 to be pulled into "new territory"

Bummer, but at least you know exactly what needs to be done to fix it

Well I have heat in my garage now, so maybe I will get around to paralleling my swing cylinders this winter

 

[Smalljobs]

Ron, I think you're right. The hose still leaks too. Meanwhile I found the perfect mandatory Jinma backhoe accessory: