Troubleshoot excavator not tracking straight. Yanmar VIO 50

[Bibendum]

JR,

I just got in from doing the same thing. I found nothing out of the ordinary in regards to the spool. That said, I was checking the main control valve, not travel motors control valves. You can see where it has rubbed in normal operation but nothing you can catch with your fingernail. The bore was also a chore to get a good look at so cannot confidently say if it was worn or had a crack between passages.

Pilot pressure was just where it should be, about 500lbs. In regards to the system relief, i have the correct pressure. For some reason I thought there was a second set of reliefs at the pump.

I’ve yet to measure any pressure at the hoses (mainly because I have no JIS fittings here, or at work) I think that will be the next course of action, tommorow. I will be interested to see what you find in regards to swapping hoses.

I believe I’ve gone down the “garden path” a little bit with this one. I work as a maintenance troubleshooter at a manufacturing facility and it’s an easy thing to do. Oh well.

Maybe the machine just doesn’t perform like I believe it should? Haha. My old Kubota would flip itself over for a joke if you wanted it to.

 

[jrhook111]

So, I only swapped 2 hoses, the 2 that are pressurized when you travel forward. So in forward travel, the right motor is being supplied by the left valve. But in reverse, those are the return lines, and the left motor is supplied by the left valve. So it confused me at first. I have a lazy left track problem, but with this test in forward, the machine went right. Then in reverse it went left. In forward, right track was lazy. In reverse, left track was lazy. In both cases, supplied by the left control valve. So, it made me scratch my head a bit at first, but I'm confident now, the left control valve is the problem.

Do you have any idea what a valve like that is going to cost? I assume you have to stick with the OEM...or does anybody make an aftermarket that is identical?

 

[Bibendum]

So, I only swapped 2 hoses, the 2 that are pressurized when you travel forward. So in forward travel, the right motor is being supplied by the left valve. But in reverse, those are the return lines, and the left motor is supplied by the left valve. So it confused me at first. I have a lazy left track problem, but with this test in forward, the machine went right. Then in reverse it went left. In forward, right track was lazy. In reverse, left track was lazy. In both cases, supplied by the left control valve. So, it made me scratch my head a bit at first, but I'm confident now, the left control valve is the problem.

Do you have any idea what a valve like that is going to cost? I assume you have to stick with the OEM...or does anybody make an aftermarket that is identical?

Not a clue. I can’t seem to find much aftermarket for mine, mind you I haven’t called the dealer. That said, when I priced the swivel seal kit, dealer wanted 650$. Found a genuine NOK seal kit online for 250$ cad. I know that komatsu had a pc27 of the same vintage that is an identical machine. Komatsu will possibly carry much of the same parts, however if you give them a yanmar part number, the number must be headed with “YM”

Worth noting, but you’re positive the relief valve is not bypassing?

 

[Bibendum]

Also, on the end of the valve bank should be a sticker with the manufacturer of the valve bank. Mine was made by “Wabco” I imagine you’re may be the same.

 

[jrhook111]

I'll see if I can find make and part# for the valve bank tomorrow. Then start the part search.

Good to cover all the bases, but I'm sure it's not the relief valve. I checked the pressures which are good, and also traded the PRV with a different one without any change.

 

[uffex]

Good day
You two guys are making a lot of questions some are easier to answer I will try to help out onece I have consumed all the teat.
Kind regards
Uffex

 

[uffex]

Good day
I have taken a look at your notes here are a few observations that may help.
Kind regards
Uffex

 

[uffex]

Good day
One attchment to go.

 

[jrhook111]

Thanks so much Uffex. Great info. And yeah, it makes sense to me that the spools will look fine while the valve bodies accumulate all the wear. So I'm 100% sure I need a new left travel control valve. I have a couple additional questions.

Do you know a ballpark price to expect on a valve like this? And is it standard to stick with OEM or are there aftermarket valves available that will fit in with the rest of the valves?

Finally, should I change both travel valves while I'm in there? Seems odd in a way, because I'm not going to change all the other valves, but travel is special. They both need to work the same or you don't go straight. If some other function is a bit slow, it's not as much of a problem.

 

[uffex]

Good day Jr
I'm not too sure which manufacturer Yanmar use for main valve supply, if we can establish this we can try and find a dealer local to you, or at least find a source. I will try from this end, let us hope we can strike lucky. As a matter of interest, if you measure the bend over 22 meters or so, how bad is the problem?
Kind regards
Uffex

 

[jrhook111]

It's bad. I would say in 20 meters I would be off by 20 degrees. I constantly have to redirect the machine when tracking, even short distances. I can't read the tag on the valve block, it is in Japanese, photos attached.

The numbers on the tag are: C0070-23202, 02-04 343. (I think 02-04 is the date.)

I also checked my parts manual for this machine (Yanmar VIO50-2), and the part number for the left travel valve is 172460-74150. Machine serial number is 21376B.

 

[uffex]

Good day Jr
Has the block three or four stud fixing?
Kind regards
Uffex

 

[jrhook111]

Four studs.

 

[uffex]

Good day
You have done a lot of work and I appreciate that you have kept me informed, I do not suggest you change the valve slice, as my study of the problem concludes this is an inherent product defect. I would not like you to change the slice and find that you have not solved the issue. I believe this is a pump bias problem in as much one pump is delivering a higher flow than the other. While we do not have a flow meter at hand, we can simply join the two pump lines together and then test for straight crawling. If this resolves the straight line problem, we have a solution which is not so expensive. Many machines have what is refered to a straight line crawling valve which couples the two lines when operating the machine in high speed. I am reasonably convinced that this is the cause and cure. Keep me informed and I will work with the solution.You may try switching the main pump lines for a test. Im not so sure how this may work out.
Kind regards
Uffex

 

[Bibendum]

That sounds like good advice to me. I will be doing that to my machine once I’ve had a nap after my backshift. How many hours on your machine JR?

 

[jrhook111]

Interesting. I will swap the pumps and see what happens. This solution would sure be a lot easier than new valves! Thanks for the advice.

Bibendum, the machine has 3200 hours on it.

 

[jrhook111]

Wow, the plot thickens. So I swapped the lines at the pump, and....now it tracks much better. A very slight right deviation but not anything to be annoyed by. Maybe a couple degrees in 20 meters.

One thing to consider, there is a hydraulic pressure accumulator on the output of P1 (as it was set up). The way the fittings are I had to swap that as well, see the gold cylinder in the photo attached. It doesn't show that in my parts manual for the machine, so I don't think it is stock. Why would somebody have put it only on 1 pump?

Here's the interesting thing. P1 is the bottom port which drives the right track, and it had the accumulator on it before I swapped lines. Now P2, which drives the left track has the accumulator and the system tracks better. I don't think the accumulator could have anything do with it, could it? I'm assuming I had a slight decrease in flow from P1 compared to P2, and then a slight increased leakage in the left valve. The 2 together made for a big tracking difference, but with the pumps swapped they are much more balanced. Any reason I shouldn't just leave it like it is?

Additionally, I could still couple the 2 pumps together, though I wonder if that would affect its function in other ways, like when trying to do simultaneous functions like bucket, boom, and stick together. Wouldn't it make the machine operate a bit differently?

Hydraulics are awesome...and tough. Thanks guys.

 

[uffex]

Good day Jr
You do not waste any time do you, for me to give you good advice I need a hydraulic schematic which is correct for your machine, that is why my previous advice was a little apprehensive.
While we have identified the cause and cure which is positive, leaving it with the changed lines, I'm a little uncertain. As to the accumulator installation, my thoughts are much as I have already stated.
If you have a contact with a manual, these will normally have the hydraulic schematic.
Kind regards
Uffex

 

[Bibendum]

Uffex,

In your experience, what have you seen as the normal/typical cause for a reduced flow capability of an axial pump? Is it more often that the valve plate becomes worn? or is it that the pistons or their bores become worn, causing a reduction in flow?

 

[jrhook111]

Hey Uffex. Gotta get this darn thing fixed! ;-)

I've attached the schematic and also the whole hydraulic section of the manual if you want more info. My machine is a ViO50-2 with quick coupler, schematic on page 8.