1. When cranking the engine, there's load in the hydraulic system, while idling, no implements activated, the pressure reads around 900 psi, 2. The return line from control valve to tank gets extremely hot, climbs to 76 degrees using an infrared gun just with idling, no hydraulic function 3. Tried servicing the main relief valve from below the main control valve, the poppet got a little groove cut around it where it seats, the most i can get out of it is 2000 psi on travel and boom up stall (HOT) 4. When the machine is cool though, the boom stall pressure reads around 3500 psi also with travel (even when travel reads 3500 psi, it still won't track fast, turn the machine or climb over a boulder) 5. Equipment won't turn, could only move when both tracks activated, but not enough power and speed to climb any incline. 6. No solenoid valves are working, (lever lock, travel speed, mode select) oh yea the swing brake works. operator said it worked fine just the way it was for quite some time. Poor thing must have suffered from lack of maintenance. Engine runs fine though. that's all i've seen so far, starter already failing due to cranking the loaded system, oil cooler not cooling oil, radiator cap missing, radiator leaking as well, travel gear oil need changing, electrical are all dead except for starting system... i'll just do what i can to get the hydraulics back in good working order. I'll update as i get the parts from the owner. (oil cooler, main relief valve, starter,) planning on checking the Main control Valve bypass valve for the return, also a safety valve on top the control valve as well, i'll also check the travel load sensing line to upstroke the pump... if anyone can also share some ideas that'll be a huge help...
If the relief valve isn't holding, it's going to heat up the oil. It would be hard to diagnose any of the other issues without the relief valve functioning normally.
I understand where you're coming from with the overheating, i must admit i was a bit overwhelmed with all the defects in this machine, like maybe this solenoid not working is restricting some oil flow, maybe that oil cooler is really the cause of the overheating (but it's really not cooling, same temp in, same temp out), maybe this, maybe that... your reply had me reassured to take this repair one step at a time. Thank you for your advice.
It sounds like the same problem that came with the PC120-6 machines that were gray market from Japan to the US some years ago. You might try turning on the key, releasing the hydraulic control lock lever and cycling the controls to see if it will release. At any rate load pressure was not being released on the hydraulic pump controls after the engine was shut down and the system was warm. Changing this spool in the main valve took care of the problem for awhile in some machines but happened again later on. If you let the machine cool down for twenty or thirty minutes the machine would start up again. PM me your email address and I'll send you a copy of an update I received years ago that was supposed to address the problem. Sometimes it did and sometimes it didn't. It is a bugger of a problem and I don't remember the work around I did to get these machines to start easily again.
Hi, I am having the exact same issue with the line to the tank getting really really hot! Did you find what the problem was in the end with your machine? Would be a great help if you can point me in the right way. I am thinking of actually putting a T on the line that goes from the valvebox to the cooler and joing the 2 up as the issue is all the hot oil is going directly to the tank and makes the machine ncredibly hot and unuseable!
Hey, I just came across a post you made last year on a Komatsu getting very very hot because of a faulty hydraulic bypass valve i believe. Did you manage to locate the problem? We have the same issue on our PC70FR-1 (zero tail version) and the hose from the control valve to the tank gets unbelievably hot! There is a small valve where this hose meets the control valve and we shut it in and when that happens the engine wont start because the system is loaded up. So that probably explains one of your problems. But what i would like to know is how to make the hot oilgo to the cooler instead of directly to the tank? Is there something else faulty thats diverty the flow to the line going to the tank as opposed to the cooler? The line going to the cooler is a big line and it goes from valvebox to swing motor and then to the cooler, so i was thinking of T'ing the tank pipe to the cooler directly. Hope thats not a stupid idea and if you can point us in the right direction. For your info one user on HEF told me they had a simmilar prob on a PC35MR-1 and they repalced the bypass valve. But i have no idea where that is to try and service it.
Do you need to pressure settings and procedure for this machine?
Hi SmokeyRiver, Yeah anything would help really. Tried a bodge last week, we blocked off the hose that goes directly to the tank from the control valve since that worked on a different excavator in the past but no luck. The thing is unbearable after 15mins and you can't even touch the ignition key its that hot! I really am stuck as to what to do. Any direction from you guys would be awesome right now! thanks
Hey, I've been away for quite some time, and I haven't gotten back to work on this particular model. I'm going to resume work on this from tomorrow though. Came back here to really refresh my memory and now saw your previous posts. Did you make any headway on your machine? I'm convinced I'll have to pull the main control bank out again, check those valves on the lowest block of it, as well as compensator valves The Komatsu uses this CLSS system where the pump increases flow once it senses pressure from the compensator valves (through a signal line from atop the main control valve to the pump regulator). High flow rate could increase the pressure in the system as well when neutral and that would also increase the hydraulic oil temps to unbearable levels, need to confirm on unloading valves as well. The pump adjustments were also a bit tricky to smoothen out the operations, got it to function at a reasonable cycle time, but the temps were way out of the comfort zone. I'm not an expert with Komatsu, especially this model but trying to follow with the service manual but still puzzling at times. I'll see how it goes from tomorrow