My bucket cylinder on my 690ELC recently started acting strange. It acts like its got a slight catch or something when i fully curl the bucket. What would cause this? I know its leeking past the inside seal(piston) some. Time to pull it apart for seals? Or? Thanks
The bucket cylinder gets damaged more than the other three cylinders because of its constant exposure to nicks and scrapes. The rod end probably has gouges in it or worst case, its slightly bent. You need to have the rod re-chromed as well as the cylinder resealed. If its bent, you may need a new rod.
That's what I was thinking. I'd check to see if that rod is bent.
I have checked the rod and can not find any nicks/scrapes in the chrome. How do i tell if its bent? If i let this machine sit for a week and pick up the boom, the bucket will swing like its not even hooked up to a cylinder. Its leeking past the piston seal I think.
If you can actually "feel" the cylinder doing something while your operating it, there's something wrong. I would take the cylinder apart and inspect the components. If there is something wrong in there, it's just going to do more damage the longer you run it. If a rod is bent enough to be a problem, it's usually bent enough for you to actually see the bend, a simple straight edge (like a level) would confirm it's bent.
My impression is the piston has come loose from the rod and is flopping back and forth. From what you describe you are most likely making metal from the cylinder and are at great risk of contaminating your entire hydraulic system. Get that cylinder off fast and tear it down. In my experience what you describe is the nut has come loose from the piston. Generally it is caused by not assembling the piston on the rod to the specified torque. DO NOT OPERATE THIS MACHINE UNTIL THE PROBLEM IS FIXED! Good Luck!!
If the nut has came off does that mean the rod is bad? Can piston seals be changed with out removing the piston if everything else is ok?
The piston retaining nut probably hasn't come off, if it had, the piston would come off and you wouldn't be able to retract the cylinder. But it could likely be loose as John C said. And if it has, it's only going to get worse. It can damage the shaft the the piston is mounted on as well as the threads for the nut. And it's possible to replace piston seals without removing piston, but I wouldn't do it. If I've gone through the trouble of taking a cylinder apart--it's getting all new seals while it's in pieces.
Just another thought, but could the bucket linkage cause it to bind up like this? Maybe un pin the rod end and run it in and out first? Thanks
My humble opinion...I'm not going to sleep good at night until I take that cylinder apart, if for nothing else, to make sure everything if happy in there.
:usaPull your suction screen deere..........
Where is the suction screen located at? I have never messed with it. Thanks
the suction screen is in the hydralic tank...on top you have the fill cap...pull off cover..drain tank first so debris does not fall in main pipe.....
Sounds like the suction valve in your control valve is posssbly not seating or is faulty. When the hydraulic cylinder is not being used the oil in the circuit is locked by the spool valve as the oil is trapped in the circuit, suction valves basically allow for a quicker fill time to the cylinder and are on the cylinder side of the spool valve so if these are faulty or not seating they allow oil to drain back till there is a neutral pressure in the line, hence the limp bucket. If you are still unsure about the condition of the cylinder best thing to do is work your way back, start by checking bypass out of your cylinder then work your way back from there. Also some excavators have a regeneration valve incorporated in the piping, this allows for quicker cycle times and allows low pressure oil to loop back into the other pipe for quicker fill times of the cylinder, if this is faulty you will get the same fault.
My 690E LC does the same thing. It also has a stutter or pause in the stick and bucket when they break over center. Could these two problems be related?
You know guys my 690 ELC done something similar. It would break over center and then pause before it would finish cureling.
That limp stick problem was common to most all the hoes in the era. Basically the oil could drain out of the stick cylinder coming in than the pumps could supply. Oil filling the piston side would take a second or two to catch up so the stick was limp until the piston side was full of oil again. Most manufacturers put in suction safety valves which were just a fancy circuit relief that would open to tank when a vacuum was felt. They also used to be called anticavitation valves. No days most manufacturers use the prior mentioned regeneration valves that route rod side oil back to the piston to prevent the suction. Other manufacturers would run two pump flow to the piston but only let one pump flow out going back to the tank. There could be problems with any of these items but my initial impression was the problem was in the bucket cylinder. I've never seen a regen valve in an excavator bucket circuit.
Sometihing else to consider guys. When you change a hose (with more than usual fluid loss) and get a airbubble in the cylinder it has a "dead spot" in the stroke. It bothered me to the point of "burping" the offending line/cyl. I not saying that the other comments aren't correct, but sometimes the easy fix is the right fix.
I have the exact same thing on my 690ELC with the stick pause. checked regen valve spool valve relief valve. Any more ideas???