Komatsu pc90-1

Hey guys looking for some help adjusting pump stroke/output on my pc90-1. Previous owner had overheat issues and function issues. He locked open the swing break solenoid , as well as the dog mode solenoid so it was in L mode. Well you know what came next, adjusting pump servo for normal output. Each function cycles as if it were in standard dig mode or faster. Now I have fixed the solenoids when I go to standard dig mode you can drag enginenway down and stall it just cycling stick and boom at same time. All reliefs are working properly as well as pilot pressures. I have the manual but not enough experience to know where to adjust pump servos. There are 4 small adjustments and two larger. I would be happy to pay someone to walk me thru it.its the last part tonget machine back to right

Basically when the yellow Y on top of pump receives pilot pressure it moves a valve that de strokes pump for L mode. However it cycles like standard mode and reacts to input quicker then it should.

I'll try to help but your pump is first generation OLCC. I don't see a TVC solenoid valve on the side of the pump so that tells my you have a two mode system. The barrel switch would be an S and an L setting. Is that correct? Can you follow that hose from the Y connector on the top of the pump back to what it connects to and take a photo of it? There are two hex headed plugs one on each pump and just to the right of the Y tube. Those should be test ports for the pilot pressure inside the pump. Do you have fittings that you can connect there. Does the machine walk in a straight line when traveling up a hill. I don't recall those machines having two speed travel in those days but if yours does let me know.

It has s/L/op modes and two speed crawl The yellow y hose go to the solenoid bank and is activated when in L mode the solenoid opens allowing pilot pressure to the yellow Y

Machine walks faster on one side as well

You mention that you have the manual for the machine. Does it have a drawing or photo that shows the names of each adjusting screw? The way to adjust the pumps is to plumb gauges into the two test ports on tops of the servo valves. You also have to plug into the pump main outputs. Later systems had modes where you checked the pressures at. They were negative control which was checked with the engine at high idle and nothing being operated. The pilot pressures at the servos would be adjusted to about 70 PSI. Then the main reliefs were set at the main control valve. Your book will have that value. Next mode is the cut out function. Those are set at about 70 PSI with the pump pressures running on the main relief. Finally the TVC function is set so that the pumps combined over relief only draws the engine RPMs down about 150 revolutions. Your machine does not have a TVC solenoid. Your solenoid is only on or off. If you have the drawing showing the adjuster names I can let you know the ones to adjust and in which sequence.

I have a pdf I could send you of manual. It would let me upload it I will see if I can break apart or maybe your email

I have the manual in PDF form. I could email you it wouldn’t let me upload it here.

Dropbox www.dropbox.com

I downloaded your book last night and just went through it looking for the pump adjustments. It tells you how the pump controls are supposed to work but there is nothing there about adjusting the output of the pump. What I'm seeing is that in S mode there is no oil going to the Y tube and in L mode there is oil going to the tube which pushes a spool to the left and puts pilot oil into the B side of the servo piston reducing the pump output. You said when in S mode the pump overloads the engine. That is telling me that there is too much spring tension pushing the spool in the control to the right which doesn't sent oil to the B side of the servo to unload the pump. So it appears to me that you need to loosen the big adjuster screws that have ground off flats on the ends to get the pumps back to working normally. At this point if you have your main relief set properly I would each screw one full turn and then try doing multiple functions at once. Say boom up and stick out at the same time and listen to how the engine sounds. If it doesn't over load the engine to the point of killing it you will know you are going the right direction on the screws. I wouldn't mess with the four smaller adjustment screws as they have to adjust both side in opposite relation. If you loosen the screw on the left side in your drawing a half a turn, then you have to adjust the screw on the right side in a half a turn. You mentioned one track was slightly faster than the other. Can you check and see if the one track does it in both directions. If so that would indicate a pump adjustment. If it switches tracks when you go the other direction it would indicate and swivel issue. If it is a pump issue you should be able to adjust the subject pump to get them close to the same. Good luck and let us know what you find out. John C.

John thanks a lot for your time and expertise. I will check to see if track is fast on same side both ways. I am recalling it does but will check it . I assume turn down the pumps will slow down the responsiveness as well? It seems like it reacts to quick to inputs as well. Track included . Will report back. Ps- what do the small screws adjust? Thank you Jake

It's been awhile since I've worked on an OLCC machine but some other things are coming back to me. Turning the pumps down should let you run the machine in S mode without killing the engine. The responsiveness may or may not come down because your system does not have jet sensors in the main control valve that would give you that true load sensing function. If you get it so the pump doesn't kill the engine, then check you cycle time by extending the stick all the way out, opening the bucket and sitting it all down on the ground. With your engine at full throttle, raise the boom all the way to the top and time it with a stop watch. It should be able to do that in about four seconds. Make sure you keep track of how far you turn each screw in case things don't work right. The machine is probably workable to some extent right now if you have to put the adjustments back. Also keep in mind that you have an old machine and the control linkages might be stuck and need dismantling, cleaning and new seals. The two small screws adjust the actual pump hydraulic load control valve which shown here. The larger adjusting screw adjusts the pump reaction to the output and pressure on the pump. This is to limit the output of the pump to less than the horsepower of the engine.

John back from my work travel and tried loosening each of the bigger adjustments with the two flats. There isn’t a whole lot there and if I tried to go one full turn out the lock nut doesn’t have enough thread to jamb and tighten. That shaft has a machined section for oring and it can be turned in but each if I turn out 1 turn the jamb nuts wouldn’t tighten ?? Baffled Thanks for the help and maybe some other ideas.

If that is the case ten turn the screw in one full turn and then do cycle times and see if it changes anything. I was interpreting the spring on the left side of #16 spool being loosened by turning the screw out. Turning the screw in might reduce spring tension. It may also be that the screw is a stop for the spool for a reduction of movement. I have seen those gummed up and in need of cleaning on newer machines. You might have to pull the retainer cap that holds the screw and look inside. If so be real careful because there is a spring in there that can fall out.

I did turn screws in and while I didn’t check cycle times pump was still dragging engine down at least two or three times more then L mode. I am safe to check cycle times in either mode? I am thinking L mode will turn back more to L mode when turning pumps down ?

Track going forward right track faster,’going reverse left track faster. However the control levers move different amounts so let me try to set those

You can leave it in L mode at least to see if anything changes. What you are trying to do is see what changes the output of the pump. What you want is a drop of about 150 RPM with it set in the S mode. If nothing changes then you will probably have to settle for what you have.

John thanks for your time. I assume the valve is stuck because those adjusters don’t really have any tension on them and when I tried to run machine with them in 1 turn and moved them back to where they were I did so by hand . I will have to take the covers off and try to get the valves moving .

Look at the diagram above to see what is in there. The lever directly engages the servo piston so it won't move. There is a rod and spring so make sure you don't lose then when you remove the cover.