I have a Komatsu PC120-6 that the hydraulics get really weak after 45 minutes of run time. It’s so weak it barely picks up the bucket. I just had the hydraulic pump professionally rebuilt last week ($4500.00) I also changed out the relief valve on the main valve block. The relief valve that’s on the pump was replaced when they rebuilt it. I’m still having weak hydraulics. I’m at lost. Any idea’s? Suggestions?
That is a load sensing system with lots of small passages to plug and plenty of electronics to foul you up. Have you checked the monitor panel for fault codes? The other issue is who is the professional rebuilder? For $4,500 all they did was put bearings and seals in and maybe lapped the plate and barrel assembly. For sure they didn't calibrate the thing on a dyno.
1. I only saw one solenoid on the pump itself. It stroked when I put 12 volts to it. 2. The digital display hasn’t worked since I bought the machine about 13 years ago. The previous owner put analog oil pressure and water temperature gauges on it when the display went out. All of the buttons work, just the digital reading isn’t visible. The machine worked perfectly and had plenty power for the last 13 years up until 2 months ago. 3.Flowdraulics in Baton Rouge are the ones who rebuilt it. They are a large company with locations in multiple states. They have rebuilt other pumps and motors for me in the past and I never had any problems. He did tell that he didn’t really see much damage in the pump when he tore it down. Nothing that was a smoking gun other than the relief on the pump was not seating right. And he put a new relief valve in. He ordered all of the new parts from Komatsu. 4. He did tell before he tore the pump down that he wasn’t going to be able to bench test it because the bell housing wouldn’t fit in the testing rig.
The monitor screens in that era used to get damaged by sunlight and you could read what was there. The only fix was to replace the panel complete. Have you tried to shift the prolix switch. It bypasses the computer and puts a set voltage to the solenoid on the pump. Does it change anything? The pump can be adjusted up but I would describe how to do it. It works on a cam in the pump and is incredibly difficult to get right. You might talk to your rebuilder and see if they can adjust it or at least show you what has to be done to increase its output.
Can you tell me where to find the prolix switch? I see only one solenoid on the pump itself and the wires go to the throttle mechanism. It’s weird because it has good power for about an hour then it gets really weak. I attached a few pictures of the pump before I took it out and after it was rebuilt.
The prolix switch is in the cab on the right side console. Sometime they are behind the vertical sheet metal panel to the operator's right side of the seat. On others they are next to the fuse panel. There are usually two switches, one is a swing brake bypass which keeps the swing brake released all the time and the other is the pump prolix switch.
We might be getting somewhere with this. I just flipped every switch that I can think of that would have an effect on the hydraulics. I also pulled the solenoid that goes to the pilot valve bank just to look at it. I beat on any solenoids that I could find. The machine seems to be a little more powerful. Not as powerful as it should be but it didn’t get so weak that it could barely pick up the bucket. I’m going to keep running it to see if it starts getting weak after it runs for a longer time.
I flipped the prolix switch and I didn’t seem to have an effect other than the buzzer going in to alarm. But it didn’t effect the power instantly.
Well, I thought we may have something but the hydraulics got weak after about an hour of running. I found a pressure sensor on the main valve block that I may change just for the hell of it. I’ll keep y’all updated. this is the pressure sensor.
Why? And why was the pump rebuilt?
The hydraulics would get weak after about an hour of use. I replaced the relief valve on the valve block and it didn’t make a difference. I then had a mechanic come look at and he said if I changed the relief valves and it was still getting weak after an hour then the pump would need to be rebuilt. I’ve had hydraulic pumps get weak on some of my other machines and they had to be rebuilt. This one acted just like the other’s
It is a load sensing system and the relief valves will seldom open at all so changing them likely did nothing. Do you have a serial number for the machine. I don't have a book anymore but it looks like you have one of the early machines with the PC valve on the bottom left corner of the main control valve. Can you stand at the boom looking back at the valve and take a photo of it?
What I am getting at is you are playing an expensive guessing game with no real testing or evaluations. I mean, it is your money and time, but I would sure be reaching or test gauges before swapping expensive parts. As well, John could confirm but I bet you can still plug directly into the ECM to see sensor data and fault codes which are likely to lead you down the correct road to recovery. If that one is anything like a CAT, the monitor is on a canbus anyway (digital) so I am sure you could find an easy way to just plug one into the system to use as a diagnostic tool. IE, they don't have wires for each gauge value, all that is digitally sent to the monitor. A pretty vital component for you at the moment.
Unfortunately there are no usable connections to the system by anyone other than a factory engineer. It is also problematic now days to find the correct monitor panel for that serial number of machine. At this point the electronics system is operationally useless. The hydraulics can be set up to operate manually and perform well enough to use. There were several different iterations of that hydraulic system so I need a photo to try to see what he has.
The serial number is 52113. The relief is in the bottom left corner of the main valve block look backwards from the boom. I’ll take a picture of it in the valve block tomorrow evening. The only picture I have currently was of the actual relief valve itself which I attached below.
Are you telling me there is no diagnostic port for dealer access? I mean, it is probably all too much for this repair as we are deep in parts swapping but I was always impressed with Komatsu's monitor/user level diagnostic data.
The only access to electrical monitoring or diagnostics is through the monitor panel.
I changed the pressure switch this morning and it didn’t make a difference. After about an hour the machine barely picks up an empty bucket. I attached pictures of the pressure switch that I changed and also the relief valve I changed.
I think I’m going to change the suction filter. I changed the main hydraulic filter when installed the rebuilt hydraulic pump. The suction filter didn’t look bad at all but maybe it’s starving for oil? I’m not sure what else to do? I have a hydraulic mechanic coming look at the machine hopefully at the end of the week.
Does anyone know if this is a open center or closed center set-up? If it’s open center, where is the valve that closes when more flow/pressure is needed?
The pressure switch tells the computer when there is high pressure when traveling in the high range. The computer will then shift travel into low range. The system is closed center load sensing. I don't recognize that main valve. The early ones had two cartridges where you are pointing instead of just that two stage main relief. If you go up to your photos of the pump, you will see a big allen screw socket with a nut that locks it in place. It is to the left of the pilot pump. In your photo the paint is gone off the nut indicating that someone has turned it. As I recall that is the cam I was talking about earlier. Again as I recall it adjusts the output of the pump. You can take the nut loose and adjust that screw one way or another and it can load up the pump and motor. Too much and it will kill the motor. Just move it a little bit at a time. The point where it is just right is small and it will change when you tighten the lock nut. I usually boom up at the same time as I pull the stick in and listen to how hard it pulls down the engine. Make sure you mark where you started before turning that screw so you can get it back in case my tired brain is remembering the wrong screw. Good Luck!
John C. Thanks a lot for all of your help. You have been more helpful than my local Komatsu Dealer. I have a hydraulic mechanic coming look at the machine at the end of the week. He should have gauges and be able to adjust the load settings better than me. Is there a way to tell if the pump is going to full stroke after sensing a load. I’m starting to think that the load sensing parts aren’t telling the pump to go to full stroke. I came across this article on the internet that may be interesting to you. I wonder if I’m having the same problem. I’ll attach the web page link below. You’ll have to scroll down the part about load sensing and differential pressure. https://www.insanehydraulics.com/letstalk/loadsensinglowflow.html
I'd wait for your hydro guy before doing anything else. You are throwing parts like a blind man shooting hoops. Do not go in blindly adjusting things without knowing/understanding more of the system and what might be occurring. But I do agree that knowing the stroke of the pump(s) will be important to know. What functions are affected and not affected? If you track forward, do you get other functions back? Does it track at full speed and straight?
That article brings up the issue of a drill in which someone adjusted a pump because the drill motor would turn slower as the system warmed up. The thing with a drill motor is that you have a directional control valve that sends oil to the motor plus a valve between the directional control valve and the drill motor that is used to control the speed that the motor turns. There is a similar possibility in this system in that load sense pressure also controls compensator actuation. In a closed center system all the valves block oil flow from the pump and the pump de-strokes to a stand by pressure which usually corresponds to load sense pressure. If you open one valve, flow will travel down that circuit and the pressure in the circuit only affects that circuit. Let's open two valves now. Oil will flow to both and the pressure that the pump sees will be the lowest pressure and oil will flow toward the least resistance. If it takes 3,000 PSI to lift the boom and 1,000 PSI to turn the house, then the boom will stop moving until the swing valve is closed again. To stop this from happening you have to put some kind of valve in that compensates for the pressure difference. First there are lift check valves on the outlet of each of the directional control valves. The lift check basically holds oil in the circuit and is between the cylinder and the directional valve so that when the directional valve opens at lower pressure that the circuit, say the boom, the boom won't drop till the pump pressure comes up to the boom pressure. The lift checks have passages that connect to all the implements that hold them closed. Now any function used has to overcome the pressure of the highest pressure circuit. That circuit is also tied to the load sense pressure that makes the pump stroke and destroke. They renamed those lift checks now and call them compensators. Your machine has compensators on all the implement circuits and it is a place where load sense pressure can leak away. There are seals on all the compensators which can go bad. The way you check load sense pressure is to have two gauges, one plugged into the pump outlet and another plugged into the load sense line for the plug. The problem though is that you won't see a leaking compensator because the pump only maintains pressure to about 300 PSI more than load sense. If load sense is leaking off, the pump is only going to keep up with the pressure in the now leaking load sense passages. The only fix we found in the past was to replace all the compensators.
Thanks also Fastline. I’m going to wait for the mechanic and let him make the adjustments. I do feel like I may have to do some troubleshooting on my own. I had 2 mechanics tell me they thought the pump was bad before I took it out. Neither one spent a lot of time troubleshooting shooting because it really seemed like it was the pump. Did you read that article in the link I posted? I’m starting to think something like that is going on. All of the functions get weak. It’s more noticeable in the boom, bucket and tracks but they take a lot more power to move.
With such an expensive component, you better have more than a 'hunch'. A fubar pump can total a machine. Very first check should be case drain. Other is heat. Filters should also be evaluated if a pump gave up. Usually a pump would not work perfect at first start, and down to a complete cripple in 45min. They are usually down on dig force at first start followed by rapid heating of the pump and fluid in my experience. Anyway, John knows those machines better than I. They are closed center which means the pump should stroke up when you activate a load. If that is done with hydraulic pressure on your machine, that should be a pressure to record both hot and cold. If it is an electric servo, find out more about how to test that. Put it to you this way, If you are trying to 'stick out', and it is taking forever, if the pump was actually at full stroke, that will be some massive heating somewhere. If that is not happening, then pumps just may not be stroking up.
WOW! That was very descriptive and explained in a way that a novice like me can somewhat understand it. Thanks. I’m trying to take the information that you just gave me and figure out a way to test the compensators. If I boom down like I’m trying to pick the track up off the ground and the boom stops moving. The pump should be at max pressure and fully stroked? Then the pressure reading on the pump should be about what pressure? And the load sense pressure should be about 300 lower than that? So if the boom isn’t moving while I’m trying to boom down and the pump isn’t at max rated pressure and the load sense pressure is greater than 300, I could assume that the pump may not be fully stroked and I’m getting some load sense circuit bleed off? I should see the load sense circuit pressure start dropping? Where would the load sense circuit pressure bleed off to? Back to the tank or suction? if I test each function like that should the load sense pressure only drop on the function with the bad compensator?
I did shoot all of the parts on the valve block, pump and reliefs with a temperature gun. None were much hotter than any other.
The only time the pump might be at full stroke is when traveling on both tracks and using a implement all at the same time. What you are missing is that the pump has variable flows. Raise the pressure high and the flow is reduced in order to hold the same amount of horsepower. The differential will stay the same all the time. If you have 1,000 PSI on the load sense line, you will have 1,300 PSI being made out of the pump. If you have 4,000 PSI at the load sense line you have 4,300 PSI out of the pump. The thing is that other controls sense the drop in engine speed and back off the pump. Usually that is the TVC solenoid controlled by the computer. On the Dash 5 line you could unplug the TVC solenoid and the pump would go to full stroke. I don't know if that will happen on a Dash 6.
Does it need to read engine speed from the rpm sensor that’s looking at the flywheel? Maybe my speed sensor is bad? I did disconnect the solenoid that’s mounted on the pump. It actually seemed like it was a little more powerful at first but it didn’t stay powerful so I hooked it back up.
I would not suspect a speed sensor unless you were having issues when cold. When it warms up and starts tripping, does it progress slowly or like a switch? The speed sensor provides input to the ECU to destroke the pumps to prevent stalls. If you grab a big bite of something when machine is cold and that engine bogs but pulls hard, it is probably working. There are default maps in the machine if the speed sensor fails, but it would not be a gradual event. Once there are enough false counts off a sensor, the ECU will flag it and ignore it.
You can check the speed sensor with an ohm meter. They will usually fail to shorting through or to no continuity. They work by creating a single phase syne wave that could be read on an oscilloscope. They fail when the bell housing fills up full of oil due to a leaking pump or rear crank seal. The bell hosing will get so hot it will burn the paint. fastline is correct in that they don't make the pump not work or work worse when things warm up. There is a fault code for a failed speed sensor but it is generally found when there is no RPM reading on the monitor panel. In your case, your monitor panel doesn't work anyway. Disconnecting the TVC solenoid and the same problem still existing would indicate the problem is somewhere else.
So if I disconnected the TCV and the pump went to full stroke/full power and it doesn’t build up to full pressure does this rule out the problem being in the load sensing circuit? Then should I assume that there is something bypassing the valves and going back to the tank? And that’s causing the working pressure to be low? I changed both relief valves that I knew about. Could a spool valve leak from the supply side back to the return side without moving the function?
I had to think about your question for a bit. The solenoid doesn't make the pump go to full flow. The TVC only limits flow when conditions are such that the engine starts to go below a set speed level because of the condition of flow and pressure. You aren't getting there in the first place.
I hooked up a gauge on top of the valve block and tested the pressure. When the machine was cold and hydraulics were somewhat powerful the pressure was 2000#. When it warmed up and the hydraulics got weak the pressure was still about 2000#. I attached 2 videos. 1 when it was cold and the other about 20 minutes later when it came up to Operating temperature.
Well I thought I could attach a video but I’m not having any luck. Anyone know a trick to attach a video?
You have to upload the video to YouTube then link to it.
I attached 3 different YouTube links. For some reason you have to click on the text link to view the 1st one. The other two appear as a video link. https://youtube.com/shorts/xB3YdEGNvqI?feature=share
What I'm seeing in the videos is that the pump is not stroking up. You need two gauges to troubleshoot the differential pressure. If you have the correct differential pressure then the pump governor are not adjusted properly and you will have to adjust the output of the pump. You really should consider trying to get a monitor panel for your machine. The electronic controls will not make your machine operate like that. I also notice that there is no alarm ringing that would indicate an electrical problem. With out a monitor panel, you are going to have to just adjust the pump output as I described above. Do you have a parts book?
I have a few questions. 1. What should I expect the pump pressure to be at full stroke and RPM? 2. I’m not sure where to hook the second gauge. I tried 2 different spots on what I thought was the load sensing circuit. But the pressure was zero. 3. My machine ran really well and very powerful for about 15 years with the monitor panel display not working. All of the buttons work, it’s just the display that doesn’t work. That’s why it has the analog oil pressure and water temperature gauges. The alarm buzzer does come on with low coolant level and when I flip the Prolix switch. I’m definitely not against getting a new monitor. I just thought since it was working before that wouldn’t be my problem. I’ll look at get one.
These are the two spots that I tried to hook the 2nd gauge. Both spots show zero pressure while working the machine.
This is where I hooked the 1st gauge that read 2000#.
Normal operating pressure is 4,615 PSI bu the book. High stage relief when the power max button on the left side joystick is pushed or you go to travel the machine is 5,041 PSI. I found my book but your machine serial number is earlier than my book. It starts at 57499. Youre arrow points at one of the check ports. I believe that if you look to the right and back just before the mount bolt you see another check port. Plug into that with another gauge. I'm not completely sure of that so be careful. You should be able to see a difference between pressures on the gauges. On the newer machines there is a port that would allow you to check the servo piston pressure inside the pump that actually tilts the block to stroke up the pump. I don't recognize your pump for sure and the drawing in my book doesn't appear to be the same.
To be able to test and predict whether the regulator of the hydraulic pump is working properly or not. We usually try to calibrate this TVC valve . If the adjustment has a clear effect, it means the pump regulator is still in good working order. The opposite means that the regulator has a mechanical failure, it is stuck. View attachment 271002
From the photos posted, his pump is different and doesn't have that type of adjustment.
I attached a picture of what I believe is the stroke adjustment bolt before I removed the pump and I have another picture of it after the pump was rebuilt and installed. There is about a 30° difference clockwise from before and after rebuild. You will have to zoom in to see the dot on the bolt. Do you think that this may be the problem? I was going to try to adjust the stroke but I have to get another fitting to be able to hook 2 gauges at the same time to compare discharge psi and load sensing psi. My kit only came with one.
That is the adjustment that I was talking about in a prior entry. You don't need gauges to adjust that. You just listen to the engine and when it draws down too much, you will know that it is working. Then you dial it back and turn it in very a small increment, tighten the nut each time, and then boom up and stick at the same time. If the engine doesn't sound like the load on it has changed, then turn the screw a little more. It is difficult to get it just right so don't get frustrated and leave at too much.
I’m going to try to adjust the stroke tomorrow. The mechanic that was supposed to come look at it hasn’t returned my call the last 2 days. So I don’t think he’s interested in working on my machine. I find when it comes to hydraulic troubleshooting that not many mechanics are interested in the work. I think they are so busy with clear cut easy part changing jobs that it’s hard to justify spending time troubleshooting. That’s why I’m trying to figure it out for myself. And thanks to y’all I may be able to.
So I adjusted the stroke and WOW! It made a huge difference! The machine was very powerful and very fast. I made multiple small stroke adjustments and worked the machine after each adjustment. It ran great for about an hour then I started noticing it slowly start getting weaker and weaker. I had a gauge hooked up and when I finished adjusted the stroke the pressure was about 3500. After it started getting weaker I adjusted the stroke again. I ended up up adjusting it until I turned it and it wasn’t making a difference so I backed it off a little and locked down. Now after 2 hours run time it’s definitely weaker, only about 2000 psi and not as powerful as it should be but it’s still more powerful than before I adjusted it. What’s weird is that it has more power at 2000psi now than when it was at 2000psi before I adjusted the stroke. Something seems like it’s leaking through more and more as it heats up. To the point that the pump can’t put out enough flow to overcome the leak and build pressure.
No you know you have a problem in the load sense line. Next thing is to remove compensators and reseal or replace.
Where are the compensators?
Here is the prolix switch. Please double check with John C.
I’m not sure that I have a good understanding of how the compensators work. From the description you gave in a previous comment of a compensator. It was described as somewhat of a load check valve. I was thinking that it was like a check valve between the valve block and hydraulic cylinder that prevents backflow from the cylinder side back to the valve block when there is higher pressure on the cylinder side. I’m trying to figure out how the compensator leaking would cause the pump discharge to be low and for example if the compensator leaked on the boom circuit would I see the boom slowly come down? If a compensator leaked would the leaked oil go back to the pump discharge circuit and possibly pressure up that circuit and that extra pressure cause the load sense system to de-stroke the pump because the discharge circuit is now more than 300psi above the load sensing circuit?
There is a single load sense passage where all the circuits are plumbed into and they intern are plumbed into a pressure section on each compensator and into the LS or load sense line into the pump. Try booming up and running the swing at the same time. Does the boom stop moving? Open the bucket all the way up and then curl it when picking the boom up, does the boom stop moving. Move the arm out at the same time you are turning the house, does the stick stop moving? I'll see if I can get a photo or two showing where the compensator is in a drawing.
Yes. All of those scenarios take place. And they are much more pronounced when the machine warms up. So would the pressure section of the compensator leak into the LS line or would the LS line leak back to the compensator pressure section? I figure that something is causing the discharge circuit to lose pressure. Either from discharge flow leaking back to the tank or suction. Or it’s losing pressure because of it being de-stroked. And that would be caused by the load sense circuit pressure to be falsely low because it’s leaking into some thing that has a lower pressure than the LS circuit?
Here is he book drawing representing operating the boom up and the travel at the same time. The valve above the letters PP and PLS are the compensator valves. Those letters correspond to the load sense circuit. No one that I've talked to over the years has had a complete understanding of what is going on inside them when the malfunction. I don't know where they leak to. Your issue is that they are draining off LS pressure to the pump. If LS pressure is 2,000 PSI at the pump load sense line, the pump will only put out enough flow to be over 2,000 PSI and it only holds stroke to maintain that amount.
Thanks you very much! I’ll have to study the diagram really hard to get a good understanding of it. So far, I see multiple seals that if leaking by can cause the higher pressure pump discharge to leak by to the lower pressure return circuit. Does the compensator valve go through the whole valve block and have to be removed in two different pieces from each side of the block?
The diagram show the hydraulic flow for booming up. I’m trying to picture the spool valve position and hydraulic flow for booming down. Pretty much reversing the flow. It seems like the boom up passages and the boom down passages in the spool valve are treated differently?
Boom down I think has regeneration and also gravity pulls it down. Only has high pressure when trying to pick up the front of the machine. Boom up also has an external holding valve mounted under the boom as I recall.
For this problem, I suggest you check the "UNLOAD" valve. There is a very high chance that there is a leak in this valve.
Here is a simple explanation for "KOMATSU PRESSURE COMPENSATION" principle.
That's the way I envisioned it to be but I was wrong about one thing. The compensators in this valve are at the inlet side of the spool valves and not at the outlet side.
Lachau, thank you very much for the diagrams. They definitely help me understand better. So in my situation are we thinking that the 125 bar orange circuit (load sense?) is leaking into the 80 bar yellow circuit (swing power) because of a faulty compensator (pressure compensator #2) and this is causing the orange (load sense) circuit to drop to 80 bar therefore de-stroking the pump? What is the purple ball that is in the 4 way section of the orange load sense circuit?
I just removed and inspected the unload valve. I didn’t see any damage. The seals looked good and had good spring tension. I attached pictures of the location of the valve and of the disassembled valve.
I also took out and inspected 2 of the compensator valves. This one is on the left track motor supply. I didn’t see anything wrong with it. I’m going to pull all of the compensators one at a time and inspect them.
I think you should not attach too much importance to the compensator valve before or after the spool valve. It doesn't affect much either. For model PC130-8, as you can see; The pressure compensator valve is located in front of the valve spool as shown below!
It is called: "LS SHUTTLE VALVE" .
So in my situation are we thinking that the 125 bar orange circuit (load sense?) is leaking into the 80 bar yellow circuit (swing power) because of a faulty compensator (pressure compensator #2) and this is causing the orange (load sense) circuit to drop to 80 bar therefore de-stroking the pump?
I want to ask more clearly: the phenomenon of pressure drop after 02 hours of working only occurs when you operate 02 functions at the same time (combined operation) or only 01 function also has a pressure drop. After 2 hours of work, with one operation, what is the pressure achieved? I think you should check each parameter separately as the attached table.
This video is after about 45 minutes total time running. I say 20 minutes in the video because it was 20 minutes after the previous video. I don’t have a video yet of after I adjusted the stroke. After the stroke adjustment was made the most pressure I could get was about 3500psi. And after a hour of run time that came down to 2000psi.
I was thinking that it probably wasn’t seal since it works good for about an hour then starts getting weak after the oil comes up to operating temperature. I thought that if was a blown seal that it would be weak all of the time? Maybe it’s a weak spring or something that expands when hot and the clearance gets bigger and allows bypass? Like a relief valve? I changed the main relief and the changed the LS relief when he rebuilt the pump. Do they have any other reliefs?
I think Lachau has way more experience here but I am wondering about the control pump. Has its performance been tested?
I think the control pump is made on to the front of the hydraulic pump and it was rebuilt when the whole pump was rebuilt? I couldn’t find a good spot to connect a gauge. But I’ll look again. What does the control pump do? This is where I connected my gauge and I got a zero pressure reading.
Pilot pump is on the back of the main pump. It is a gear pump and supplies oil that makes all your pilot functions work. Hand and foot controls, things like two speed travel, swing brake and control of the swash plate angle in the main pump. Pilot pressure used have a pipe plug on the dual connection fitting opposite of the relief valve cartridge attached to the pilot pump. You can follow the outlet hole and see if you can find another place to check it at. Pilot pressure was set at around 426 PSI. There is no rebuilding of that pump. You just replace them if they won't hold pressure spec. I use a 1,000 PSI gauge to measure the pressure with. You usually take them apart to see if they are worn out. I've never seen one bad enough to be a problem. Komatsu did away with those and went to a pilot pressure reducing valve mounted on the inlet of the main control valve years after this model of machine. Did you see any marks at all on any of the compensator parts?
Sorry!! So sorry!!! I have never heard or read the name "LS relief" in any document?!!!
I didn’t see any marks or scares, the O-rings looked good but maybe a little too flush with the edge of the compensator barrel? But they were all about the same. I still have 3 more to take out and inspect. My wrench was too fat to get a good bite on the compensator so I’m going to grind it down a little.
Lachau. I’m sorry. I kinda just guessed that it would be called the LS relief. I’m not even sure if I know where the LS system starts or stops. Haha! The arrow points to what I thought was the LS relief. There was a relief that was made onto the pump that the guy that rebuilt it said that it wasn’t seating when he checked it with air pressure. He said he put a new one in. The same arrow points to what he said was the relief he changed?
That's the pilot pressure relief that I spoke of above.
@Mr.Blanchb as Mr.John C said. That is the pilot pressure relief valve.
The mechanic came look at my machine this evening and after a bunch of troubleshooting and some adjusting he believes that one of the spool valves has a busted o-ring. There was one valve that looked like a relief valve that he wasn’t sure about. It’s on the very bottom right side of the valve block and on the counter weight side of the valve block when you’re standing with the boom to your back and facing the counter weight. He suggested that I pull the valve block and look at the spool valve seals. I was thinking that I could remove the hydraulic tank then I would have enough room to pull the spools out from one side. It looks like it would be easier to pull the hydraulic tank than to pull the whole valve block? Can the whole spool valve come out from one side of the valve block? What do y’all think?
Never don that before. Let us know how it turns out.
Can you take a photo of that valve??
So we have established that you didn't replace the main relief valve that is in the valve block?
I did replace the relief valve in the main block. That was the very first thing I did before I pulled the pump and had it rebuilt. This is a picture of the new relief installed.
This is the valve that the mechanic questioned. It was dark last night when he was looking at the machine and he was using a flashlight so he couldn’t troubleshoot as good as he wanted.
I pull 2 of the spool valve so far. I’m not sure how they are supposed to look but I didn’t see any o-rings on the spools themselves. I can feel grooves where I thought o-rings should be. Both spools o checked were exactly the same. No o-rings. They were for the bucket and the stick.
I forgot to reply but I was questioning the diagnosis of "spool Oring" and how someone came to that conclusion? Did you check the parts schematic to see if any even exist there? I'have never seen any and they are usually precision machined to tight tolerance. You would have to have basically a complete blowout to cause your symptoms. Did you test the control pump and pressure at an end of spool? My opinion is either spools are not opening all the way due to not enough actuation pressure, or the pump is losing stroke. You should determine which it is. If a spool is not opening all the way due to a loss of control pressure, the pump would not upstroke as it is not needed. Like getting to the basics, you should determine if main spools are actually going to max throw when commanded. I tend to think something is up on the control side.
The online parts book “My Komatsu” website doesn’t show o-rings. I didn’t test the control pump pressure yet because I didn’t have the fittings to hook up a gauge. I’m going to get the fittings next week.
What is this adjustment for?
I forgot to mention that the other day after I adjusted the stroke and the pump pressure went to about 3500psi. I noticed that the pressure would swing and the hydraulics would sputter when under a heavy load. The last 2 days the pressure would only drop to about 2800psi after warming up. That was better than dropping to 2000 like it was before. The sputtering seams like a relief is opening or like the pump is starving for suction flow. I cleaned the suction strainer and changed the filter. I just wanted to mention those things.
You must love to take stuff apart more that I do.... Is the guy that recommended orings on your spools a real tech or a friend? Sometimes free advice gets expensive. Anyway, I really don't know what you are experiencing but I would say if you monitor the pump outlet pressure when things are sputtering, you may see pressure that is too might now and has no where to go. The closed center pumping arrangement is designed to try to match demand with pump output. It is very possible that you now have a mismatch. Did you record anything you did? Hydraulics, like water, can carry a bit of inertia so if you operate a function, demand goes up, pump stroke tries to follow along. Then you stop the function but the pump has to respond to that. It can cause a small spike in fluid pressure but usually not crazy. Comb that control side and see what you find. Somewhere in the book it should indicate what pressure is required for full stroke of one of the main spools. You want to ensure you can get there. That's probably right where I would start. Like you may well find good pressure off the control pump, but maybe you have a pattern changer that got weird and now leaking over, causing low pressure to functions. IDK, just throwing ideas here. As for the suction side of the pump, forget about that. You would likely know something was wrong. Cavitation is not a pretty sound.
That is the differential LS pressure adjustment.
Fastline. Thanks for your input and help. I really do appreciate it. 1. I really don’t want to or have the extra time and money to have to keep taking stuff apart. I wish that it would be an easy fix and the first thing I tried would fix the problem. 2 The mechanic is a guy that has been referred to me by many people including the company that rebuilt my pump. They will take his word over anybody else’s if he finds that the pump is bad even though it was just rebuilt. when you ask anybody in our area about who to call about hydraulic problems, this mechanic is the one everybody suggested. According to him he has 35 years of experience. Now mechanic’s just like operators and any other craft will tell you about their experience and knowledge makes them the best and that everybody else’s opinion is stupid. 3. I know that I’m not a mechanic. And I don’t try to represent myself as one. I do 90% of my own mechanic work, I am mechanically inclined and normally I can fix whatever I’m working on. That said, I know that I have the least amount of knowledge and experience as compared to the people that I’m talking to on this website and locally in my town. So I’m at the mercy of other people. If I disregard and don’t do something that someone suggest then they will wash their hands of me and not want to help. But on the other hand if I do something that a different mechanic doesn’t agree with then that mechanic wants to wash his hands of me. So I’m kinda stuck between a rock and a hard place. 4. I ordered some more test fittings so I can test pressures in different spots and multiple pressures at the same time. They just haven’t came in yet. As soon as they come in I will check the control pressure. 5. I did try to call my local Komatsu dealer before I pulled the pump and after I pulled the pump. One time they didn’t show up or call. The next time they said that they we’re backed up with work and couldn’t tell me when they could get to me. I have a good repor with them and have been a customer for over 20 years. But mostly buying parts.
You everyone that might have more experience in this system once had to learn it too! I freely admit I have never even been in a Komatsu X system! At this point I would say in your down time, I would be soaking up any books or educational videos on design as it may help you better understand how the system works. Anyway, enough of the pep talk, what I would personally do is identify a function that is known to have a problem (boom up maybe), and tie into the spool control line. When cold give it full stick, observe performance as well as pressure. When performance drops off, observe that pressure. If pressure has dropped off significantly, that will tell you right there the spool is not moving far enough, thus the pump won't upstroke because it's not supposed to. If that pressure is low, then and only then go back to the pump itself. if that pressure is down, it doesn't always mean a bad pump. That particular pump is fixed displacement so if the volume demand from it goes up beyond what it can do, pressure will drop out. Then we start playing the game differently. Now if pressure to the spool remains good, we know the spool is getting full throw and probably a 95% chance the pump is not upstroking for some reason. That would go back to the LS circuit. LACHAU is far more knowledgeable on these machines and his pictorials are classroom perfect. I am only advising from general fluid power knowledge, but my experience is limited. I would be much more help with electrical....that is my specialty. It was my understanding the -6 had electric proportion valves but I don't see them in there. If they do exist in that machine, that brings another layer. Probably the easiest way to know is if you have hydro hoses in the cab going to the sticks in a manifold block, prop valves are not there.
I’m going list the history of events in chronological order. 1. I heard a pop.(I forgot about this and didn’t mention it before I thought it was the relief) 2. Hydraulics started getting weak after it warms up. 3. I changed the hydraulic oil filter and oil. I had 32 weight and went to 46 weight. 4. I called the local dealership. No show. 5. I called the company that rebuilds the pumps. They don’t do field diagnostics and they referred me the the mechanic. 6. Mechanic came out and looked at the machine and thought it was a bad relief. He showed me where it was and said that if that doesn’t fix it that the pump probably needs to be rebuilt. I replaced the relief with a new one and no change. 7. I removed the pump. And brought it to the shop. 8. 2 months later they finished rebuilding the pump. He told me when I brought it that he wouldn’t be able to put it on his test bench to test it because the flywheel housing wouldn’t fit on his test equipment. So he couldn’t test it. 9. Installed the newly rebuilt pump and brought it out to a job and it performed the same as before. Weak when it gets warm. 10. Posted my problem on this forum. 11. Bought a hydraulic test gauge kit. And the tested pressure after warm up was about 2000psi. I posted a video to this site. 12. I adjusted the pump stroke. When the machine was warm and the most pressure I could get was about 3500psi. 13. I pulled and inspected the unload valve. I didn’t see anything wrong. 14. I pulled and inspected all of the compensator valves. I didn’t see anything wrong. 15. I started noticing that wasn’t dropping all the way down to 2000 anymore but the hydraulics started to studder when I put a heavy load on it. But it wouldn’t studder with a light load. Also I noticed that it would run about 2 hour before getting weak and studdering. But I had enough pressure to actually do a little work even after it got weak. 16. Mechanic came out after dark and troubleshooted with a flashlight. I’m thankful that he came out. He put the old relief back on to see if it would act the same. (No change). He adjust the valve at the bottom right of the valve block when facing the counter weight. (no change). He adjusted the LS pressure up and down. (. It got weaker when he adjusted it down. And stronger when adjusting it up. But it wouldn’t get over 3000psi. He made a few other adjustments and disconnected a few lines while running but it didn’t change anything. When he left he thought that it sounded and felt like a relief valve or something somewhere else was bypassing back to the return side. He thought it may be the spool valve bypassing. 17. I pulled 2 of the spool valves just to look. I didn’t see any o-rings. After I got home I looked up the part break down and didn’t see any o-rings in the part break down. 18. Waiting on fittings to test the control pressure.
Once I get the right fittings I will test all of the parameters in the list that Lachau, JohnC and Fastline provided and I make whatever adjustments I can to get everything within those parameters. I will post the result’s when I’m done.
The pop sound is curious. Is it something you heard and might have felt in the machine? FYI, the controls are all pilot operated. There are no electric proportional controls on this model of machine. The LS valve sets the difference between pump outlet pressure and the load sense pressure controlling the pump. In general it is supposed to set the sensitivity of how fast the pump reacts to changes in the outlets from the valves to their functions. In practice, it usually doesn't make a lot of difference. There just has to be a difference between the two circuits. There are no O rings on the spools for directional control. The O rings only seal oil into the system and keep it from leaking out. I am curious about that valve cartridge in the bottom right side of the main control valve. My book doesn't show it and I don't recall ever seeing one there in the machines I've worked on. Maybe Lachau shows it in one of his books?
You need to document any changes you make! If you turn an adjuster, record it! You now have a stutter you didn't have before. That is likely from the tuning. You need to be able to return things back where they were. The bang is VERY important as there is no seal or Oring that would do that. I would lean towards a spring. Try to recall exactly what you were doing, which functions, when that happened. I would not expect a broken spring to misbehave only when warm though. It's odd!
The pop was somewhat subtle a little less than opening a champagne bottle. I don’t remember feeling it and I didn’t notice anything operating any different immediately after. So I didn’t think much more about it. It was over a week before I ran it again and it slowly started getting weak over the next few times running it before I really notice it. I had the inline fuel screen that’s in the fuel line banjo fitting get stopped up a few times before this and when it was getting weak I thought that’s what it was again. But after I checked the screen and fuel line and I didn’t find any pluggage I started realizing that it was a hydraulic problem. I really can’t recall the exact function that I was using when it popped because I use multiple functions a the same time.
I think I found the valve that the mechanic wasn’t sure of. Do y’all know what this is for? It looks like another relief valve?
If I have the right valve picked out in my service manual, I think they are calling that the LS Selection valve and your diagram does show seals and backup rings. I also see a cone popper (#6) of which I've seen a lot of problems with over the years. It is tied directly to the LS circuit and might very well be a reason for your problems. It appears to need a hook spanner in order to remove it. If you take it out and take it apart, check the line around that cone. It should be a perfect line around the cone in one place. If the line has an odd shape, replace the cartridge as a unit. I see plenty of O rings and backup rings in the diagram as well. Good Luck!
I just pulled part of the valve in question. It takes a 1-9/16” or 40mm wrench to get the part off that screws into the valve block. I have a 1-1/2” and a 1-5/8”. Neither work. I went to 5 different places today trying to buy the right wrench. No luck. A crescent wrench won’t fit. So the spanner nut wasn’t really that tight and the outer body unscrewed fairly easy. I just couldn’t get the main part off from the valve block. The spanner nut just seats an o-ring. The outer body must be adjustable either in or out and when it’s set right you lock down the spanner nut to seat the seal. I felt inside of the part that I couldn’t get off and it felt like a little tappet with a little nipple and it’s loose in there easily moved around with my finger. I’m going to take it off again tomorrow and take some pictures. So when I put it back in I didn’t know how far it should be screwed in before locking it down with the spanner nut. So I guessed. When I cranked the machine and tried to operate it, it would barely lift the boom off the ground. So I screwed it farther in and locked it down and tried running it again. The boom came up with plenty power. It was dark outside and I ran out of time to run it until it warms up. But I’ll be able to run it tomorrow to test it. I’m not sure how to adjust this and I don’t want to mess anything up. The adjustment definitely made a difference. I just don’t know what’s right. I’m going to try to get the rest of the valve off the valve block tomorrow to see if it has any internal seals or something else that doesn’t look right.
Komatsu's technical documentation is troublesome!!! We must refer to this document to be correct.
I had to ask my staff to rummage through my previous photos!!!
Damn! Thanks so much Lachau! So I thought I changed the main relief but I actually changed the LS relief. Is that a picture of the LS or the main relief? It looks like the one that I changed. I’m going to pull the MAIN relief today to inspect and take pictures. I’ll post them when I’m done. It there a certain way that I should adjust the main relief when I install it?
I removed the main relief and inspected it. I saw a little light scaring. It wasn’t really enough to hook a finger nail on. But it was rough. The needle had some uneven wear. I’m not sure it is bad enough to cause my problems but I think I’m going to change it out with a new one just to see if it helps. I attached a picture and a video.
The parts guys must love you by now....
A new one will be set close. The ring around the cone that I can see in the photo shows the cone is shot. It cannot be saved. It is the pilot that operates the relief. If it is leaking there the pressure will be lowered. The wear on the poppet at the bottom shows the affects of dirty oil. Sometimes you can just polish that poppet by chucking it up in a drill press or a lathe and use some crocus cloth to smooth everything out. Better to replace the whole cartridge. That is a two stage relief so when you are traveling it goes to a higher pressure setting. That poppet shouldn't have wear like that as the pump is supposed to destroke before the pressure gets that high.
I’m having hard time visualizing the path of the oil when the relief opens. I can follow it through the cone but after that it looks like it has to pass by a tight tolerance machined fit sort of like a spool valve? When I change it out with the new one, do i have to adjust it a certain way or should it come already adjusted from the factory! After I change it out should I idle the machine down when I first start it just to make sure that I don’t overpressure the system? I probably have to reset the stroke adjustment, LS pressure and control pump pressure. Then gradually work my way up to full throttle and make adjustments as needed?
You have to remember that many things have been "adjusted" by now. There is no telling if this is induced by the problem or solution at this point. I have no clue where this is going but the "pro" recommended spool Oring replacement so..... I just hope the OP finds a real pro at some point to sort these issues out. OP, you are still going on and on playing the parts swapping game instead of real diagnostics. Pressures and temperatures alone should point you (or something) to the real issue. It's really frustrating to watch someone drown at sea. You have realize that when warm, your boom would hardly move at full stick! Let's just assume that ALL that oil is shooting through that little relief, that would create noise, heat, etc. All things you indicate are not happening. I hope I am wrong but I am not buying this. IMO, either pump is not upstroking, or control side is not commanding spools to full tilt. Have either of those even been verified? I mean seriously, this is little different than someone swapping an engine before checking the air filter. You need vital info. ALLLLLL things that would have been available to you with a monitor. I am no hydro pro, but I learned from one of the best (now dead) that you never try to sort the high pressure system without confirming the pilot system is right. I am imploring you to examine the basics from the front to back. You are guessing. I never do that. I at least want some firm data that points me to a diagnosis. Then I go in looking for what I believe to be the issue. Not taking everything apart hoping to find a clue. IDK, rant ended. I am just frustrated to read this play out.
Install it and try it out with your gauges installed. If it works, it should bring the machine back to life. You said earlier that the old one improved things. Next thing you have to do is re-set the stuff you messed with. The TVC you know how to do. The differential or load sense pressure is with the allen head screw on the pump. You want about 300 PSI difference between the pump outlet pressure and the load sense pressure. Checking the main relief means jacking up the pump output over the main relief so I wouldn't worry about doing that. The relief won't create a lot of heat because the system is load sensing. The pump will destroke because the pressure won't build beyond the pressure the main relief. That's the idea of a load sensing system.
Hope to be helpful. Good luck.
I ordered a new main relief valve, it’s not coming in until the end of November. I’ll let y’all know if it fixes the problem after I install it. I did tighten down on both adjustments of my existing main relief thanks to Lachau’s documents and it made a the max pressure increase by about 300psi. It made a very big difference in my track speed. But it still gets weak after about an hour of running.
You are approaching the finish line. Now, the problem is that after an hour of work, the machine becomes weak. I want to ask after an hour of work, what is the temperature of hydraulic oil? How long ago did you change the hydraulic oil? The story of the machine becoming weak after a period of work will make us rethink many different components in the hydraulic system: the main pump component (cylinder, piston, swash plate, servo piston, LS valve, TVC valve...), the control valve component (UNLOAD valve, the LS Bypass valve...)
One more information for your reference: KOMATSU excavators usually have a function called "CUT-OFF FUNCTION" . This function can also sometimes cause the maximum pressure of the hydraulic system to not reach the desired value. You can try it by unplugging the connector of the "TVC solenoid".
I took multiple temperature readings from multiple spots with laser temperature gun. So they were all external readings. The hottest temperatures would be about 180°f. There wasn’t a big temperature difference from one spot to the other. The hydraulic oil has been changed twice. Once at the very beginning of troubleshooting my problem I changed from 32 weight oil to 46. I did this because of the oil temperature. Then I changed the oil again after I had the hydraulic pump rebuilt and then reinstalled. I was thinking that the oil is running a little hot but I thought that it was because something like a relief was prematurely bypassing. I’m hoping that when I do fix the problem that the oil will run cooler. I did unplug the tvc solenoid and flip the prolix switch a couple of weeks ago. John C had mentioned that I should try it. I didn’t notice any effect when I did it. But I think that was before I adjusted the tvc stroke. I’ll try unplugging it again now that I have the stroke adjusted.
In my opinion, such hydraulic oil temperature is higher than normal! Normal hydraulic oil temperature is about 140°F. Have you ever checked the hydraulic cooling system?
I have no experience with this model but that temperature seems awfully low. I would normally expect a temperature somewhere around that of the coolant, up to 185°F or thereabouts, or am I missing something.?
I noticed that according to the manufacturer's instructions the temperature of the hydraulic oil and the temperature of the engine coolant are different?!! The manufacturer requires that when checking the standard parameters, the temperature should be as in the attached table. In fact, I have found that if the temperature of the hydraulic oil is 180 degrees F, the O-rings and seals will quickly deteriorate.
In addition, I also refer to the characteristics of Kobelco, Hitachi machine... and even another 3rd party ( https://hyprowira.com/en/blog/maximum-temperature-of-hydraulic-oil ). Do all say the best working temperature of hydraulic oil is 140 ~ 158 degrees F?????!!!!! So where is the truth ?? I really want to hear from all of you on this matter.
I pressure washed the the fins that I could see on the hydraulic oil cooler. ( I made sure not to flatten the fins with the water pressure) Some of the other fins are covered by the A/C condenser and I couldn’t get to them. They really weren’t that dirty. The engine fan and belts are good and the engine runs at 180°. I was going to mention the other day that after I adjusted the main relief as tight as I could comfortably. ( I kinda felt when the seat bottomed out on both adjustments and stopped there). The Machine built up more pressure (about 4300psi) and tracking was a lot faster and more powerful. But I noticed that the engine water temperature would come up to 200°f. Like it was working harder. It didn’t sound like it was working harder or lugging but the temperature came up like it was. I was thinking that whatever is causing my weak hydraulics is the same thing causing the hydraulic oil to heat up?
I recall asking about heat earlier in the thread and OP said it was "fine". Seems like that area needs review. OP mentions temps of 180F with an IR gun, which means external surfaces. Actual fluid temp may be closer to 200F, which is just too hot. Probably one of the best places to test temp is the inlet side tank on the hydro cooler as it is Aluminum and should give a closer IR value. Excessive heat is HUGE MAN! That needs chased. Maybe Lachau can confirm if these would have a function inhibit (limp mode) in the case of hydro overheat? I use a FLIR camera and it might be worth renting/borrowing one. People think and IR gun tells the story, but FLIR is a color coded full image that will take you right to the source of the heat in seconds. I have fixed hundreds of things, even electronics with it. You also want to check your cylinders, motors, etc. I also don't know about you switching to #46 oil. That is generally not a good idea as that alone will cause more heat. Was the old oil black and burned looking?
I have seen plenty of older machines with high hours on the clock run a lot warmer hydraulic oil temps than a new machine would obtain. After making sure that the area between the hydraulic oil cooler and the engine radiator was clean and making sure the standard operating parameters were set to factory specification, the hydraulic systems still ran warmer that 140 F. I just figured for the most part what has become normal considering worn internal parts and leakage of the systems along with normal internal and external plugging of coolers and radiators. Also consider that the monitor panel on this machine doesn't work and the owner's perception is based on using an infrared thermometer on external parts of the system. In my experience doing inspections on thousands of excavators, the most obvious signs of a chronically overheating hydraulic system is leaking packings on the boom cylinders. It is a dead give away when first walking up to the unit. Here is a revealing quote: The pressure is about where the pump is supposed to destroke. From that statement I would suspect that Lachau is correct but it will have to be confirmed after the relief valve is replaced. Also from experience I would say that using a pressure washer on the hydraulic cooler is not the best way to clean the radiators. It tends to turn the dust into mud and concentrates the blockages in between the hydraulic oil cooler and the radiator. Older models of Komatsu excavators had a plate that could be removed underneath that space and material could drop out. As I recall on the Dash 6 line, the plate was no longer there. In other words material would just fill that space and there was no longer an easy way to remove it.
Are we thinking that the main relief is bad and causing the loss of pressure and the excessive heat in the hydraulic system? Or are we thinking that there’s something wrong with the cooling system and the loss of pressure is because of the breakdown of the viscosity of the hydraulic oil at high temperature? Or we thinking something else? I’m able to see between the A/C condenser and the hydraulic oil cooler and I don’t see anything built up there. I can’t see between the hydraulic oil cooler and the radiator but I can feel air blowing through it from the fan and the engine wasn’t running hot so I thought that the external parts of the hydraulic cooler were not plugged?
My point is to stay the course. Replace the relief and then monitor operation. I don’t remember if you have a way to monitor engine temperature while operating the machine.
I can monitor engine temperature and oil pressure. And also monitor hydraulic oil pressure. The hydraulic temperature I have to measure manually.
uhhhhhhh, that sure looks like a monitor!!!
The color in the background of the unit indicates it is a dead monitor display. The buttons work and that is it.
I realize but was my understanding it was missing! Not working is a big difference! I bought one of mine with a dead display. Took about 3hrs to revive it. In this case, and the fact that there is no much vital info available in that monitor, I would sure make that repair a priority! I do board level repairs so that would not concern me much, but surely there are repair houses if someone decided the monitor was the issue?
Let us know if it is something you can fix or you know of someone who can do it. I don't know of anyone in this area of the country that has been able to repair or provide and aftermarket source of replacements. Last time I got one it cost around $2,000. There are different parts depending on the serial number of the machine and it replaces the button panel as well as the display.
Not sure if that is directed towards me but the bottom LED in the display appears lit so there is something awake in that monitor. What probably sucks most is having the actual machine gives the best chance at a repair. I would bet with the tech resources of Lachau and my electronics background, it would be a simple deal. At the moment I am leaning towards something inside the monitor because that LED is lit. Typically I am about 90% crippled in repairs because I can't get a PCB schematic and tracing boards becomes quite fun. In the case of this machine, I would probably not sleep for days just to get this monitor going because that thing can likely indicate what is really going on with the machine.
I agree with this view of Mr. John C. I think we have to replace the main relief valve first. Yes; This is one of the reasons why the performance of the machine is reduced. In addition, because the machine's performance degrades after a period of work, we must definitely pay attention to the cooling of the hydraulic system. We just need to check, if it's wrong, then correct it, if it's good, then fine. I don't think it's futile or a wasted effort.
Fastline. All of the buttons and the lights associated with the buttons work. The digital read out portion of the display doesn’t work. Lachau. I will double check the cooling system. I’m thinking that the only things that I could check is the cleanliness and air flow through the cooler and make sure that the fan is blowing as much as it should? I thought I saw something in the parts breakdown that showed a cooler bypass valve? Maybe I can try to check that some kind of way? Can you think of any other things that I could check?
Speaking from lots of experience here, I would probably unplug that monitor so you can remove it, then open it and reseat(unplug/replug) any connector you can find. It is an extremely common strategy we use in IT/computer work. Contacts eventually lose good contact due to thermal cycles, temp changes, oxide layers, etc. Just reseating things strikes a fresh contact and if anything changes in performance, note that. I would fight tooth and nail for that monitor to work because those have very valuable data in them that will likely help you with the machine. If not now, it will in the future.
I will unplug I will disconnect any plug that I can find associated with the monitor and reconnect them. I let you know if it works.
Note what I said. Just unplugging the monitor won't fix it. Probably tried 100x by now. You would need to open the monitor. There is likely a stack of a few PCBs in there. And cables or small plugs you see, unplug and reset them. See if this gives any changes at all. Sometimes it does not bring the "big fix". but it changes something that gives incentive that the hunt is on.
The display panel is ruined by ultraviolet rays that burn the panel out. It was a known problem that Komatsu supplied a filter plate for to prevent the issue way back in the nineties. Once burned there was no repair, only replacement. On the overheating, remember that you changed the TVC setting so you will likely have to back that off some and set it by cycle times of the boom up function. That will also affect the amount of heat being generated. Don't lose and sleep over it until you get the new relief installed and see what you have.
I agree with that, thus why I have been covering my switch gear with a towel. It appears this is an LCD not LED display and those are more tricky to repair as I would need to verify actual display specs for replacement, and that certainly is not a DIY type project. Those would use a solder header on the PCB. Still worth the effort on something like this IMO.
Guys, Chinese magicians do retail this LCD monitor. We bought one to replace the PC120-6 monitor. Its quality depends on your luck or not!
Thanks Lachau. I’ll look into replacing the monitor display panel. Since we are on the topic of “Chinese Magicians”. I attached a screenshot of part of the conversation I had with the place I bought the main relief valve from. I had asked them if the relief valve was already set and ready to install right out of the box. And if so what was the relief set pressure that it was calibrated too. This is their reply. Based on Lachau’s documentation. It says the low end should be set at 1.27 mpa (185psi) and the high end set at 2.94 mpa (426psi). They are saying theirs is set to 320psi? But they say it ready to install right out of the box? I asked her to double check with their engineer and she did. What do you think? I’m kind of confused because I thought that the set pressure would be somewhere around 4500psi. Maybe I’m wrong on my conversion from mpa to psi? Or I’m not understanding how the settings work on the relief valve? I attached a copy of the document that Lachau posted. And I also sent them the same document.
OMG!!! I remember very well that I posted the pressure settings for this machine already!! The maximum pressure of the main relief valve has 2 values: 1/- In normal mode is 31.85 MPa (4619.45 psi). 2/- In power-max mode it is 34.79 MPa (5045.86 psi).
The 320PSI to 426PSI range is the pilot pressure relief cartridge and not the main relief.
Lachau. I definitely didn’t mean to misquote you. I do remember that you posted the document with the different max pressures for each function. It was the same document just like the last document that you posted. That’s why I’m confused about the main relief pressure settings? I must be reading this document wrong.
I worked all night last night and didn’t get home until 5:00am this morning, so I didn’t get much sleep. Maybe that’s why I’m so confused about this.
This is working principle of 02 stages main relief valve.
for more detail.
Lachau. Thank you soo much!! I’ve been straining my brain trying to figure out how this relief worked. Now, after reading this and comparing what I’m reading to the pictures numerous times I think I finally got it. there is a very small flow going through both relief orifices even during normal operation. It’s not until the flow increases more than the orifice design that a D/P is formed creating a low pressure on the down stream side of the main poppet thus causing the spring to compress and the poppet to move pass the oil passage holes to let HP oil go into the LP chamber. The higher pressure setting just increases the amount of pressure needed to create that D/P. Thanks again for your knowledge, patience and understanding. So what are your thoughts on what the suppliers engineer said about the set pressures on the relief valve that they are sending me? The 320psi?
The main relief valve finally came in and I installed it. I cranked up the machine at low idle and it put out 4500psi. I was a little worried about over pressurizing the system and causing the relief valve to open so I backed down on the TVC adjustment. It really didn’t make a difference on the pressure. The pressure stayed at about 4500psi when loaded even the engine was at idle and even with the tvc adjusted down. I slowly increased the rpm’s to max and the pressure wouldn’t go above 4500. So I guess load sensing is working and de-stroking the pump. The movements were very slow so I increased the tvc adjustment and the movement speed got much faster. The tracks are much more powerful, actually better than they were before I had problems. I adjusted the tvc while working the machine and based the adjustments on the engine load/speed. I did make adjustments on the LS adjustment but it didn’t have that much of an effect. So all that said, I do believe it’s fixed now. And the main relief valve was the culprit the whole time. I’m at a part of my job that I don’t need the excavator much. So I still need to make time to run it all day to see if it continues to preform good. I will measure the hydraulic oil temperature and pressures after running it for a long time to see if it gets hot again and loses pressure. But so far I ran it over 2 hours and the temperature and pressure stayed perfect. So good that I blew a hydraulic hose. I’m going to need to make a few more adjustments because the movements are fast and powerful but the levers response is a little delayed. I’ll keep y’all informed. I would really like to thank everyone on this forum that helped me. Without y’all’s help I wouldn’t have got it fixed. The knowledge and experience y’all have and information, direction and documentation that y’all provided is so valuable and appreciated by a guy like me you can’t even imagine how much I appreciate it. So thank you again Lachau, John C and even Fastline.
Congratulations you have solved the problem with your machine. Your joy is also our joy (the people who participated in answering this post). To be honest, I was a bit apprehensive at first (since you said you're not a professional excavator repairman) so we weren't sure if our posts would help you. But in the end, we realized that you have a very good background, so you have put our suggestions into practice very well. Once again, congratulations on your success.
"Adjusted LS but it doesn't have much effect". You don't feel this effect on speed and power but it has a different effect, bro. The slow response of the levers is a consequence of the incorrect adjustment of the LS valve.
Hi good people. I know this is couple years old but I go throu the same deal with my 120-6... This 8 pages are so much help to me.. After machine is hot it will not turn and loose power. I order all filters and pressure relief valve... If I have to I will rebuild the main pump myself. Thank you good people for all the good information and knowledge. May God bless you all and your family.
It will most likely be a closed center system. Get your technician to check the load sense pressure to the pump. If he specializes in hydraulics then get him to flow test your pump on the machine and check it to Komatsu specifications. Unless he is very familiar with the machine and the fittings required then he would most likely need to make 2 trips to your machine so that he has the right gear to set up for flow testing the pump. This at least will isolate the fault to the pump or main control valve.
I asked for flow test but he don't have the equipment I will contact komatsu Indianapolis to come and check the machine... Can main pump be rebuild by me or has to go to shop??
If your on a very tight budget and you have experience in doing similar work like engine overhauls then get yourself a pdf copy of the workshop manual and have a thorough read up on the disassembly and assembly section of the pump before giving it a shot. What ever you decide on just don't buy aftermarket parts or cheap rebuilt pump units and allow for the cost of pump testing and setting after the repair so you know everything is sound and running to its specification.
theres a load sensing valve on the pump. You need to rebuild it and use the correct seals and o rings etc. The main culprit are teh wear rings and they look fine but bypass fluid causing a bunch of issues like the one you mentioned. Afterwards there is. calibration process to make sure it's set right.
Is that the load sence valve??
Hi technician came and did test but didn't have more then 3500psi on tower with valves. (top) He said there is bypass to pamp for some reason. He did drain case and it was a lot fluid come out. I asked him for any valve would cause that he said no you need new pump.. I will order me a new ls valve and try that before I get new pump. What are your thoughts?? Thabk you all in advance because I really need to fix that machine and finish my house.. May God bless you all.
The composite seals on your LS Valve all looks intact so this may not be the issue. Case oil leakage from the pump can be mistaken for the pilot pump relief oil that relieves into the pump casing. Without being able to flow test the pump leaves you at a cross roads to whether the issue is within the pump or the control valve. For that reason it would be a good idea not to purchase another pump until you can confirm that your current pump is the underlying cause of the issue.
Hi and thank you. My I ask where the pilot pump relief valve located?? Thank you guys you are more help then I expect
Order one I will see if that helps. Thank you
Any idea what are them 2 codes mean sir?? Thank you in advance
Fault code details and diagnostics pdf attached. I wouldn't think there would be any issues with your pilot relief. It is designed to relieve into the pumps case and can be mistaken for making the main pump appear to have excessive bypass. Best thing is to remove your pump and inspect the internals for wear. you wont need to fully strip the pump but if you need any help I can step you through the process small steps at a time providing you can upload photos as you go. You may want to consider investing in some test gauges and fitting if you are going tackle it your self. I can advise you for what you will need for that as well.
Hi sir yes and thank you I will take it out and see what is inside and inspect if there is something wrong. I will definitely need your help and if I need to pay for your service I will. May God bless you and your family
I know this is an ol der post but do you know the part # for main relief and does it all come together one or have to order each little part I’m having exactly same issues also have put new pump in runs 1 hour then slows down