I have a Komatsu sk820-5 that has 330 or so hrs. I used it all day yesterday to move dirt and for about 1 hr today and it was working perfect. I go to dump a load of dirt and the bucket will not curl down until it went to at least 25-30% throttle. Once I dumped the dirt it would not curl back up until I gave it throttle and then it was jerky. The loader arms lift just fine at idle. I checked the hydraulic level and it is spot on, there are no leaks, I just changed the hyd filter about 80 hrs ago. It uses 10w30 oil for hydraulics and I didn't change it since the book said it was not required until 500 hrs. What do you all think? Clogged line? Even though the loader arms work fine could a clogged filter be the cause? Any suggestions would be appreciated.
I'm not a Komatsu owner but here are a couple thoughts for you to consider. First of all the loader function is ok. This tells me that supply from tank to pump and from pump to control valve should be ok. It sounds like it is definetly in the bucket circuit. Have you eliminated all mechanical problems? I have seen a bad bushing/pin (tight or seized) make the function jerky and require more hydraulic pressure to move it. Are the bucket pins taking grease? Are they free? After that a thought is that a load check valve is stuck or damaged inside the control valve on the bucket circuit. Next would be a cylinder has partially come apart internally. Usually if a piston comes off a rod the oil will just bypass through the cylinder and the function will not operate but if the piston has just backed off alittle bit it is possible for the function to work, slowly, with increased pressure/flow. Good luck, hope this helps. Z
thanks for the info Thanks for the checklist of items to look at. I did check for an overtight bushing and I even disconnected the front cylinders from the front bucket mechanism. The cylinders with nothing attached would not move at or near idle speed but again the remaining hydraulics were fast at idle. As before they would move fast once the engine was at 40% or more so it may be in the circuit. I have called a local heavy equipment mechanic who is supposed to look at it in a couple of weeks so I will post when he find out the problem.
Often when fluid is bypassing in a cylinder it gets hot. Not to be confused with regular hydraulic oil temp. Run them and compare temperatures between two cylinders if one is bypassing inside it should heat up fairly quickly. Perhaps your spool is not shifting all the way? or something went though and damaged it letting oil bypass?