I recently bought a Kobelco sk120lc mark IV to use on my farm, I have experiance with all types of heavy machinery and bought this machine knowing the bucket cylinder was in need of rebuilding as it had no digging power. I rebuilt the cylinder even though I found no seals that were obviously wore or damaged and put back together with the problem still unsolved. Bucket has plenty of pressure on dumping side and all other hydrauiocs are good.
Serial# is ypu1359, any help would be greatly appreciated as I am trying to rebuild after a tornado and am on a time limit. Anyone else have trouble using Kobelco's website?
Could you swap the hoses to the bucket cylinder easily somewhere? if the bucket will curl but not dump, then you know you have a valve problem. Is this pilot valves? Have you looked at the valve linkages?
Sounds like an issue at the main control valve. stuck spool maybe? bad relief maybe. Here is link to the site I use for Kobelco http://partstore.cnhexcavators.com/us/parts-search.html#epc::home
Yeah, swap the hoses first if it's easy, then swap the port reliefs, see what happens. According to the online parts book should be about 4,800 psi on either end. looks like the bucket spool is the center one of three spools in the valve block.
I swapped top and bottom bucket relief valves as suggested by a Kobelco tech, no change whatsoever. Is there something inside spool valve to look for specifically?
The spool itself should freely slide back and forth. Pull off the spool cap and check for debris, a broken spring or o-rings the need to be replaced.
I pulled spool valve off but did not see any o-rings other than the cap seal, maybe this is the problem. I am planning on swapping spool valve off another function to see if the problem follows the valve. I tried looking up spool valve to look at seals/o-rings but have not had any luck getting a clear drawing. Correct me if I am wrong, but if problem follows valve its the valve, if problem stays where its at, it would be in the controls? Also if I have no response by swapping spool valves I intend to swap lines on bucket at the top of the stick. I expect problem to reverse as I have enough dump pressure to lift machine off the ground.
There are no O-rings on the spool, if the bolt is tight and the springs are not broken and the spool slides free in the bore it's good. IF the cyl is good and you've swaped port relief valves you can check pilot pressures after you've swaped hoses. wes
Send me your email address and I'll send you the service manual. Hard for me to find time to reply this time of year.
Thanks so much for all your help finaldrive, email: [email protected] . Update, pulled bucket spool valve again and inspected, still don't see anything that jumps out at me. I was going to swap spool valve with one off another function but none of the rest of them have the same hose fittings. Therefore I swapped hoses at the cylinder and as expected the problem reversed itself. So here is a recap: originally my Kobelco SK120LC had no digging pressure on the bucket, it would move some but very slowly and would fall limp when I turned loose of joystick. It did have dumping pressure and would lift machine off the ground. I swapped the top and bottom port relief valves with no change, I have inspected spool valve twice and as said earlier swapped hoses at the cylinder and problem reversed.
I sent you an email with a link to download the service manual.
Just to double check, you swapped the port reliefs from both ends of the center spool of three, correct? At least that's what it looks like in the parts book.
Lantraxco, yes, I swapped center spools of three, top and bottom with no change. They are actually still swapped as I saw no need to switch them back. Last night I removed another spool just to see if I could notice any difference from the bucket spool, no luck. Removed hose from top of spool cap and actuated joystick: In the dump position hydro fluid shot out of hose, in dig position nothing. Does this trigger any flags?
So you get fluid from the hose for one end of the spool, but nothing from the hose for the other end? That's an issue with the pilot controller.
All right I give ,I have swapped lines on pilot controllers, problem switched too. I have also pulled the main relief valves and negative relief valves clean orfices reinstalled no dice, although digging pressure may have increase a touch but still not even close to adequate and bucket is still falling back when joystick is released. Bucket does not fall back when dumping. Starting to get a bad feeling as to why this machine was forsale.
Hold on a minute, when you switched lines on the pilot controller, did it just reverse the control so it worked backwards or did the problem switch from the curl to the dump function or vice versa?
Lantraxco, I swapped bucket and stick control hoses behind cab. The problem followed the hoses, went from right joystick to left.
You need to do some R&R on the main valve bank. Sounds like a load check is missing, spring broken, or jammed
Could it still be a port relief valve even though that swapping them had no effect?
Not likely, unless, no offense, you somehow swapped the wrong port reliefs by accident?.
Did you get the service manual I sent you?