Kubota hydraulic cylinder seal replacement, "slide jig" and "correcting jig"

joea99 · Aug 5, 2021

Got a leaking dipper stick cylinder. Done a couple simple cylinders before, so ordered a seal kit. Then decided to look at the WSM, where they specify a "slide jig" and "correcting jig" to install the piston seal, apparently over an O-ring, in the same groove.

Apparently the only way to install these correctly is to use the "slide jig" to ease the seals on then coax them into the correct final dimension using the "correcting jig". While they specify some differing dimensions depending on what cylinder is under repair, there is no indication there are 3 different sets of jigs and no hint, that I can see, as to part number.

I could take the cylinder and kit to a hydraulic shop, but, being the experienced (cynical) old codger I am, I figure they would simply "wing it" and when I reinstall it and it leaks, they will blame my kit.

What's a poor fool to do?

RickB · Aug 5, 2021

Soften the seal in (very) hot water, install it then put a properly sized piston ring compressor over the piston and seal. Let it cool and complete the assembly.

oldnslo · Aug 5, 2021

Rick has the best approach for this type of seal. You just have to be careful to not stretch the seal to much in one area and cause it to thin out. Suspect the slide jig is a tapered thimble to help stretch the seal evenly over the piston.

rswyan · Aug 6, 2021

What I did was heat up some hydraulic fluid to the point of boiling and then drop the seal in it to soften it up, then carefully work it into position using my fingers (painful) and a thin dental pick.

After I got it into the groove the piston was wrapped with some closed cell packing/padding foam and a hose clamp was placed around it and tightened up. It was then placed in a zip-lock bag and put in the freezer for about 12 hours.

After I removed it from the freezer I was able to reinstall it with no issue (avoiding catching the seal on the edge of the cylinder bore when putting it back in the tube)

Did both curl cylinders that way and it worked fine.

Make sure to slather the seals on the piston and gland nut good with hydraulic fluid before attempting reassembly.

joea99 · Aug 6, 2021

May give those methods a try.

I had been looking at piston ring compressors for small engines, made ib plastic, but they are too small. Larger ones are all metal and seem likely to damage the seal.
Come to think, I have some old Teflon tape left that we used to coat rollers on microfilm machines to prevent scratching the film. Maybe some of that on the inside of a piston ring compressor would work?

A few hours in the freezer has help me press bearings on.

I mighy give a go at making, or getting made, the jigs the WSM spells out. Today it's only the dipper, but all the rest are all about the same age and the wipers are getting sad, so a little time spent on jigs now might save me grief in the long run.

joea99 · Aug 12, 2021

I've got a CAD file for the "slider" "re-sizer" and a "pusher" with expandable fingers to push the hard seal down over the "slider". I did not do the work, but supplied the specs from the Kubota WSM. OCD? Maybe so, but it's been a learning experience. The file allows various sized to be specified.

3D printed them and they look promising, but the sizer and slider are probably better made in steel. I'm going to work on the 3D printed parts a bit more in different materials, including a Carbon Fiber material I just got and see if I can get a smooth enough and strong enough part to not be concerned about ruining the seal.

I do not know any machine shops or machinists that would be willing to make these parts, but would be interested in hearing if there are.

Dave M7040 · Aug 13, 2021

Messicks, a large Kubota dealer, provided these instructions on how they install seals without the two jigs.

Read attached pdf file

Dave M7040

ROUSTABOUT · Aug 13, 2021

joea99 said:
Got a leaking dipper stick cylinder. Done a couple simple cylinders before, so ordered a seal kit. Then decided to look at the WSM, where they specify a "slide jig" and "correcting jig" to install the piston seal, apparently over an O-ring, in the same groove.

Apparently the only way to install these correctly is to use the "slide jig" to ease the seals on then coax them into the correct final dimension using the "correcting jig". While they specify some differing dimensions depending on what cylinder is under repair, there is no indication there are 3 different sets of jigs and no hint, that I can see, as to part number.

I could take the cylinder and kit to a hydraulic shop, but, being the experienced (cynical) old codger I am, I figure they would simply "wing it" and when I reinstall it and it leaks, they will blame my kit.

What's a poor fool to do?

Put ring on. Put a radiator hose clamp over it and tighten down. I worked at kubota. Never used special so and so's.

wdchyd · Aug 13, 2021

only thing I can add is we use a small square (1” x 1”) square of thin shim stock (.010”) or a piece of alum soda can to put under the worm on the hose clamp to protect the seal when tightening the clamp. Works perfect and quickly.
No need for all this special tool stuff.
While boiling seals and sticking hyd rods in a freezer works it’s not necessary.

joea99 · Aug 13, 2021

Thanks for all the advice. I will probably follow it (I can get pretty stubborn), but first I'd like some opinions on the condition of the cylinder. The piston itself, metal part anyway, look fine.

I posted this on its own in this forum, but it has not response as yet. I guess even if it is questionable, at this point, I may as well give it a try? I cannot "feel" and ridges, using a makeshift feeler, a stick of wood with a finish mail though it.