Repacking/rebuilding a cylinder

[slowrev]

The relief valve is usally on the opposite side of the valves as the cylinders are........
So if you have the valve in the center position and snag something on the bucket, the pressure generated by the bucket pushing on the cylinder has to go somewhere.

Ben

 

[john_bud]

The relief valve is usally on the opposite side of the valves as the cylinders are........
So if you have the valve in the center position and snag something on the bucket, the pressure generated by the bucket pushing on the cylinder has to go somewhere.

Ben

You would think so, but no. The pressure just builds up and usually something bends or breaks. For me, it usually bends -- then breaks !

jb

 

[KJM]

Even with the loader connected to the tractor, there is no fluid visible anywhere. I would think a relief valve popping would dump fluid somewhere under the tractor. I don't know that much about it, but I'm imagining something like a PT valve on a water heater where water is dumped until the pressure goes down.

The relief valve will just steer excess fluid back to the tank (gearcase). So you won't see external leakage. Everything you've posted is consistent with damage to the internal seals, and given that this happened after an "impluse load", it is feasible that the sealing edge of the seal has been damaged. Basically, the seals are just O-rings (all of mine are square section O-rings) that sit in a land machined on the piston. If you impluse overload the system, my guess is that the seal might get slightly rolled and then pinched. This might nibble the edges of the seal and eventually it looses the "seal" property... DIY cylinder re-packs are not hard at all. I used the information from these forums to get the courage to do my first one! There is a lot of info on doing it, but the essence is:
(1) undo the "top" pin to free the rod from the tractor
(2) use whatever (pipe wrench for the desperate) to unscrew the cap (just loosen it)
(3) remove hoses, remove lower cylinder pin
(4) unscrew cap and remove the rod+piston. Do this somewhere you can deal with the oil.

The seals are all pretty straight forward after that. In another post I claimed it would take me 20mins to do a seal. I did the last one in 10mins

If you do this yourself, I'd highly recommend checking the bores for scoring and for lips. Impulse loads might also have pushed the piston into the cylinder making a lip that just cuts the seals. The loader cyls on my 20+year old B7100 combo have frighteningly deep score lines (or so it seemed to me). The hydraulics guru I took them to just scratched his head and asked what I was worried about... Replacing the seals more frequently would be way cheaper than new shiny cylinders.. His view was that the only thing he'd be fussed about were lips..

Hope this helps a bit!
/Kevin

 

[chanceu]

Thanks to all. My biggest question was answered in that it isn't a huge deal to repack the cylinder. The seal kit cost around $13 so I think I'll give that a shot before I have to pay someone to do it.

 

[john_bud]

KJM did a great job on explaining how to do it. One tip, loosen the cylinder cap while the cylinder is on the tractor. It's hard to clamp a stubborn one in a vice and not hurt it.

You also need to be super clean. Pressure wash the outsides down real good before you start. Then clean the bench down and remove all junk and stuff (or is it just me with a messy bench?), then put a clean sheet down and do your work on that. You can usually get a clean sheet from Goodwill for a couple bucks. Much cheaper than the hall closet...don't ask...

Use a sloppy amount of hyd fluid on everything when assemblying. It will help in keeping seals from tearing. The rod/piston assembly usually needs to be compressed with a piston ring compression tool. 10-15 bucks at an auto parts store. The rod assembly goes down the cylinder with the same action used to set a hammer head on a new handle.

Good luck!
jb

 

[JerryG]

The reason that the seals are blowing is because you have the bucket angles down to much. You aren't blowing the seals because of the hydraulic pressure, you are blowing them because of the amount of force that the tractor is putting on them. The bulk of the force needs to be on the pins where the bucket is mounted. By having the bucket angled the way that it has been, all or almost all of the pressure from the tractor pushing is being directed to the packing in the cylinders.

 

[KJM]

KJM did a great job on explaining how to do it. One tip, loosen the cylinder cap while the cylinder is on the tractor. It's hard to clamp a stubborn one in a vice and not hurt it.

Thanks I guess I didn't make that clear enough - which is why (2) was unscrew (loosen) the cap and then (3) remove the lower pin. The caps on my cylinders were done up by a 400lb gorilla, and there is no need for them to be insanely tight. Tight, but not a 4' pipe wrench and 6' length of cheater bar tight! The tractor is a fine anchor for loosening the caps!

The other thing I probably should have said is that the piston might be solid (small diameter cyls have solid pistons) or it might be a 2 part assembly. If they are 2 part - you need to undo the nut on the end of the rod. The nuts on mine were all welded to the rods (previous owner(s)!!!!!) - I guess that won't be the case for you.

The last(!) thing - you should be able to pull the rod/piston from the cylinder by hand (slowly). If you can't - be careful when you reach for a compressed air gun to "assist". Don't ask about that

/Kevin

 

[chanceu]

Thanks for all the information. I don't expect it to be too difficult especially since it was just done a few months ago.

 

[john_bud]

Thanks I guess I didn't make that clear enough - which is why (2) was unscrew (loosen) the cap and then (3) remove the lower pin. The caps on my cylinders were done up by a 400lb gorilla, and there is no need for them to be insanely tight. Tight, but not a 4' pipe wrench and 6' length of cheater bar tight! The tractor is a fine anchor for loosening the caps!

The other thing I probably should have said is that the piston might be solid (small diameter cyls have solid pistons) or it might be a 2 part assembly. If they are 2 part - you need to undo the nut on the end of the rod. The nuts on mine were all welded to the rods (previous owner(s)!!!!!) - I guess that won't be the case for you.

The last(!) thing - you should be able to pull the rod/piston from the cylinder by hand (slowly). If you can't - be careful when you reach for a compressed air gun to "assist". Don't ask about that

/Kevin

Actually, experience has shown that the caps should be loosened first. If the top pin is off, the cylinder can flop around. And, yes the 400# gorilla must have a job at the cylinder shop!!.

The cylinders I have mostly dealt with don't come out by hand. They don't even budge much if any by compressed air (safety strap them...) I usually have to use a come along to get the rod and piston out. Unless, it is totally toast. Then they do come out pretty easy. These are cylinders with Vee packings and they are persnickety.


jb

 

[gemini5362]

I would think long and hard about doing that job on a machine that was still under warranty. I have scraped hard arkansas rock lots of times with my tractor and done what you described I have yet to have any damage. I would take it back to the dealer again and tell them that it broke again. If you rebuild the cylinders yourself and something happens to them at a later date your warranty will be useless. I realize not much can go wrong with cylinders but I would let the dealer fix all problems with the machine. That is one of the reasons you buy from a dealer is so that you get a warranty. If the dealer refuses to fix it then get that in writing and fix it yourself at least that way you have some recourse if something else goes wrong.

I also agree with the earlier poster. The relief valve is set so that if you put too much pressure on the cylinder (and to me that includes packing) then the relief valve opens up and allows the fluid to go back to the tank. If the relief valve is working correctly I would not think that you would hurt the packing in the cylinder. The relief valve does not open up and stay open dumping fluid to the ground. It is a spring loaded valve that when the pressure exceeds the spring setting the valve opens up and bypasses fluid back to the tank until the pressure drops below the spring setting then the spring pushes the valve closed and holds it closed unless the pressure climbs above the setting again.