More Back Hoe maint. Cont from prev.

[strevethan]

So it goes on. As per the previous thread things all seem very tight on this tractor. I could not get the nut off of the end of the piston, so I had to get it to a large bench vise and use a breaker bar & 30mm socket . after removal I did find scratches on the piston, very small & I suspect should not cause harm. However I did find 10-12 small chips inside the cylider when the piston was removed. They look like machining chips to me. I found no apparent source of the chips inside the cylinder. My guess is it is debris from the original assembly & likey caused the scratches on the piston. So I think I need to re examine the seals that at first looked perfect. Maybe there are micro cuts in them. If so I am hoping to lightly hone out the scratches on the piston and cleam and re-assemble with new seals. My thought is the piston should not contact the cylinder wall itself but that the seals should do that job, yes?

Any and all thoughts would be a great help.

 

[Breeze]

Glad you got the cylinder removed.

The piston is chrome plated and for it to seal properly under immense pressure, it needs to be completely unblemished. I don't recall the reason you were taking this down in the first place. Was it leaking? If it was, I hate to spend your money for you but it is unlikely that new seals will last if you have scratches and or have ground on the rod, in any way.

If you replace the piston you have two routes to take. Buy a factory part or have a new one made up by a machine shop that does this. I used to stock chrome shafting and we could manufacture a new piston or entire hydraulic cylinder for half the cost of an OEM part.

I searched "Hydraulic cylinder repair manufacture and a bunch of shops were displayed. For example: http://www.jmhtrailers.com/Hydraulic-Cylinder-Manufacture-Repair.htm These guys even offer re-chroming of pistons which may be an even less expensive route to take. Good Luck!

 

[strevethan]

Ouch again, The advice I ask for is not always easy to listen to.

It was "sagging" on me, the main boom that is. It still had enough power to function but it would not stay in place, I would have to continually bump the lift to even drive without it sagging to the ground.

When I first looked at the cylinder and piston inside it looked perfect. I still think it looks amazingly good its just the small scratches on the front corner of the piston itself. The rod looks perfect. I even thought that it might not have been the cylinder leaking at all but the main valve? Could that cause boom drift or sagging?

So these mysterious chips that look a lot like machining chips, are the only odd evidence I have. The rod still looks untouched and
IF I hone it at all it will only be on the piston front corner It has a machined radius at that edge.

The old seals do not seem to be scratched or cut or even worn a great deal. The new seals look identical to the old ones.

The reason I am even attempting this all, is that I have the week off and several projects and crew members showing up this week. Plus materials for a pattio & deck and several other major landscape "must haves". So my only other option is to rent a piece of equipment and send this to the pros as many have suggested I do from the start.

Thanks again,

Scott

 

[Breeze]

If it wasn't leaking at the seal, well, it wasn't leaking at the seal and the ram is probably ok.

I'm not a hydraulics guy so possibly someone will chime in on your "bleed off" issue.

 

[strevethan]

Fair enough & your help and experience has been very much appreciated. My current quandry is do I lightly hone the front edge of the cylinder & put it back to gether or do I do the responsible / wise thing and replace the piston.

One way or the other I should get a better feel if I put it back together and it still leaks down.

I will wait until Monday and take it to the local dealer to have a look at it.

Many thanks..

Scott

 

[Breeze]

My current quandry is do I lightly hone the front edge of the cylinder & put it back to gether or do I do the responsible / wise thing and replace the piston.

I'm a little confused. I thought you said you had scratches on the rod. You have a piston seal, a rod seal and a wiper. Pressure against the piston seal extends the rod, pressure against the rod seal and opposite side of the piston seal compresses the rod in a double acting cylinder

The most common damage is to the rod surface which will damage the rod seal and cause leakage around the wiper seen when you are compressing the rod into the cylinder. The piston seal is normally protected and the rod doesn't come in contact with the cylinder ID so this seal will leak only if worn from use, or due to heat, or possibly crud in the hydraulic fluid?

Pressure on the piston end, keeps the rod extended. If it is bleeding off, it is either leaking around the piston seal or somewhere upstream in the hydraulics that should keep the fluid under pressure on that end of the chamber. If the rod seal is leaking, you'd see fluid around the wiper. If the piston seal is leaking, you wouldn't see leakage, it would be escaping into the opposite chamber, the one not under pressure, and be contained by the rod seal.

Damage to either the rod surface or cylinder ID will eat the seals, in any case and touching either up, by hand is sketchy.

 

[strevethan]

I abosultly concur with all that you just said. That is exactly what is happening, it "leaks " down" the boom sags, but there is no external leak at all. That is why I suspected the piston cylinder seal imediately. I have looked very closely at the piston and the score marks on it extend to the edge of the gland, if that is the right term, so I think it is best to replace or remanufacture the piston. Since Im clearly down for the near future I plan to take it to the Kubota technition and have them fully diagnose and likely rebuild the cylinder. It may still be in the valve / control system but the cylinder is clearly in need of cleaning, rebuilding. So tomorow will tell just how expensive this is going to get. I dont know if there is any waranty but it looks clear to me there was machining debris involved. (3-1/2 years old now) Since I elected to disassemble I am assuming my waranty, if any, is void.

I was really expecting to find a clear seal failure but that is not entirely certain. So I will proced from here,

Scott