EX120-2 system base pressure too low

[Jason Klassen]

Hitachi EX120-2 Excavator Service Repair Manual
This is the Highly Thorough manufacturing facility service repair work guidebook for the Hitachi EX120-2 Excavator Service Repair Manual, this Solution Guidebook has actually specificed images as well as action by step instructions

Hey Max, thanks for the link but I already have the manuals for this machine, both in PDF and hardcopy.


What I really need is info on how much is too much when it comes to wear in the main control valve. I have been reading that a lot of hydraulic systems are designed with 3-8 um (0.00012-0.00031 inch) of clearance between the spool and the bore that it rides in. Seems like once its a little scratched it would be all over in terms of internal leakage.

Does anyone have experience with salvaging control valves? What can and can't be done or when it's too late and time for a new one.

 

[Jason Klassen]

SECTION 01 GENERAL INFORMATION
Group 01 Preautions for Disassembling and Assembling
Group 02 Tightening Torque

I don't understand what you are trying to get at here. I have the procedure for setting the circuit relief pressures from mg2361.

My workshop manual only has tightening torques and the painting scheme in the general information section.

 

[Jason Klassen]

Hey John you said this earlier in the thread...

Is there anyway that the spools got put in the wrong holes?

I have been looking back at some of my pictures from when the main control valve was apart and comparing them to the parts diagrams I can find online. This first pic is of the boom, arm and thumb spools. The bucket spool was still in the control valve, so not in the picture unfortunately. From what I remember it looked like the thumb spool though.


This next picture is from a parts diagram.



To me something looks off. In the diagram the thumb and the arm look the same, the boom is a little different and the bucket is the most different. What do you guys think?

mg2361 do you have a clearer diagram that I could compare my spools to?

 

[mg2361]

mg2361 do you have a clearer diagram that I could compare my spools to?

Unfortunately, no. But what I do have is that the spools have a number stamped on one end. I have what spool number goes to what port.

Propel spool (left or right) - 32
Swing - 37
Bucket - 24
Boom - 4 or 04
Arm - 25
Auxiliary - 6 or 06

 

[Jason Klassen]

Awesome, thanks! I will pull the spools and have a look.

 

[Jason Klassen]

So... the plot thickens! I pulled the spools today and had a look. Only one spool had numbers that matched the list.

Supposed to be | What I have
Propel spool (left or right) - 32 | 30
Swing - 37 | ? (scribed on 9)
Bucket - 24 | 26
Boom - 4 or 04 | 27
Arm - 25 | 28
Auxiliary - 6 or 06 | 06

Here are some pics.

 

[Jason Klassen]

This is a pic of the tag on the main control valve. Maybe someone can tell me if this control valve even belongs to this machine?

 

[mg2361]

So... the plot thickens!

UH-OH! I don't have any listing for anything other than the EX120-2/3. Maybe my list is obsolete?

 

[Jason Klassen]

UH-OH! I don't have any listing for anything other than the EX120-2/3. Maybe my list is obsolete?

I love these problems... not! I feel like I always get the ones that nobody else has ever had.

I was really hoping the numbers on the spools would be correct but just in the wrong order. With all the numbers except for the thumb being different I decided to google the numbers on that tag. When I put in the last number (4304717) I get results for a ex100-2 or ex100-3 main control valve, not a 120-2/3. They must be really similar if not the same because all the hoses and pipes bolt up.

Is there a way I should go about manually verifying which spool should be in which hole? Try to measure the distance from the bottom of the spring seat to the internal openings in the control valve to see if the lobes on the spools line up?

 

[Jason Klassen]

Ok I have not tried measuring the spools yet but I wanted to run another theory by you guys. I was picking up some bucket ears for a digging bucket I am modifying from the local water jet guy and he had some ideas about my track problems.

I can move foreword and back but when I try to turn with one track or the other it will do about an 1/8 of a circle and then just stop. Maxes out at about 4000 psi in p mode but does not move.

He thought it might be that my center joint is leaking internally. Does this sound reasonable? The center joint is dry on the outside.

Earlier when I posted the thermal pics of the center joint, one of the right hand travel motor hoses was warmer than the others while idling. When looking from underneath that hose is still warm but the case drain from the left travel motor was warmer weird ?!

 

[mg2361]

Internal leakage of the rotary manifold is a possibility. Usually when they leak internally, you also have a mis-track.

 

[Jason Klassen]

Hmmm, I don't seem to have a mis-track issue but the seal kits are not very expensive so it might be worth doing. I read on a final drive site that if you run a case drain test on both motors and they are with in spec then the rotary manifold could be the next suspect. The kit looks like it has lots of seals, so plenty of room for weird problems to occur.

 

[John C.]

Does your machine have two speed travel? I've seen plenty of times the range was stuck in high range and of course the machine wouldn't turn but it traveled straight.

 

[Jason Klassen]

Does your machine have two speed travel?

It actually has 3 speeds. Turtle, slow and fast. I think turtle is supposed to be 60% of slow. A while back I tried pushing the speed buttons while tracking. I held the track leavers in the same spot and pushed the buttons. It seemed to pick up and slow down depending which button I pressed. So I think speed control is working but the differences in speed between the modes seemed too small. I feel like I had to concentrate a little too hard to notice the difference.

 

[John C.]

Three speed units that I have worked on use the pump outputs to change one range. Say low to mid is the pump output and too high done using the range selection in the motors. The high range is done usually by using pilot oil controlled by a solenoid to change the tilt angle of the swash plate in the motor to minimum stroke. Minimum stroke means faster rotation of the motor but less torque. Typical issue is either the solenoid and signal from the computer or leakage between the range signal in the swivel into the drain port. I've also seen leakage in the servo piston for the swash plate in the motor cause the issue but that usually only affects one motor at at time.

 

[Jason Klassen]

Thanks John, I believe you are correct with the function of the 3 speed control. Sounds like this swivel joint can cause all kinds of issues. I think I am going to have to order a rebuild kit.

 

[Jason Klassen]

Well, I received the seal kit for the swivel joint and proceeded to install it. When I opened it up it looked like someone had already been in there. The seals were not too bad. I put the new ones in anyway and its all back together now. The problem with not being able to turn is still there.

I am going to check the travel speed time to see if it is stuck in high range. There is a spec in the manual for how much time it should take to cover 20m.

Fast 13sec + or - 1sec
Medium 21sec + or - 1 sec
Slow 34.5sec + or - 2sec

I am also now looking into the proportional solenoids. I have noticed that when I boom up and arm in at the same time the boom won't move until the arm is finished.

Also while tracking I cannot boom up, only boom down.

 

[Jason Klassen]

Just finished doing the travel speed test. I tested each speed twice.

Fast: 23, 24 seconds
Medium: 27, 28 seconds
Slow: 31, 31 seconds

Looks like there is a difference in the speeds but it is not nearly what it should be. Only the slow speed is close to what it should be.

Also in slow speed it takes a couple of seconds for the tracks to start moving after the levers have been pulled. In medium and fast the tracks start moving right away.

At the end of the test I ran a couple more passes with the travel proportional solenoid unplugged, it made no difference to the times.

Mistrack is supposed to be measured over the 20m distance also. After running 8 passes I would say the machine ended up about 3/4 of a track width over from where it started. I going to call it good. The actual spec is no more than 230mm off course in one pass.

Any ideas on what these times indicate?

 

[Jason Klassen]

I just finished testing the Pi Pressure. The results are interesting!

Spec is 512 psi + or - 7 psi
I got 690-700 psi. The needle fluctuated a little. Test is supposed to be done in P mode (full throttle). It showed 690-700 psi through the whole throttle range from idle to P.

The pilot pressure is set at: 720 psi idle, 780 psi P mode. Looks like pressure reducing valve is reducing the pressure and holds it steady through the rpm range but, it is clearly not reducing the pressure enough!

This Pi Pressure is put on one side of the variable pressure compensated valves. The proportional solenoids then act on the other side. Since my pressure is too high the proportional solenoids can't do their job properly which I think explains my travel speed and combined operation issues.

Now to figure out how to bring the pressure down! Might have to get a new reducing valve.

 

[Jason Klassen]

Ok, I pulled the pressure reducing valve apart today (controls Pi pressure) and removed the shims. 1 0.5mm shim and 2 0.2mm shims. Put it back together and got 350 psi. Then put the two small shims back in, no change, put the big shim in and no change, still 350 psi. I then added a 1.75mm washer to the stack and got bang on 500 psi.

I am thinking that a few months back when I was putting new orings into everything I could think of the pressure reducing valve must have gone back together with the spring not being properly seated. It makes more sense that I would have to shim it to increase pressure because I had to with the pilot pressure regulator and things usually loose pressure over time not gain it!

Now to the travel speed. I tested the travel change over pressure and got 400 psi. According to the specs I should be getting full pilot pressure there, which in my case is 720-780 depending on the rpm.

I know the travel speed solenoid is working because I got the 3 different times to cover 20m posted above. Maybe the little spool is sticking that the travel speed proportional solenoid acts on. I am pretty sure its fine though because I have had all the proportional solenoids off to put new orings on the sleeves that the spools ride in. The proportional solenoid itself is a new one so I gave the adjustment one full turn in but the pressure did not change.

Any ideas?

Here is a section from the trouble shooting. I added some notes in red.