Chinese mini dumper stalling in reverse-what to check?

[2manyrocks]

I bought this Chinese mini dumper at auction for a little over $1,300 because I wanted an inexpensive track machine to work with in a tight area infested with honey locust thorns. The machine appeared to be unused and still had inventory tags on the rubber tracks when I picked it up from auction.

The problem I'm having is the machine stalls out completely and kills the engine when the control levers are moved to reverse by pulling back on them towards the operator position. The engine also stalls slightly when the controls for the front bucket and the tipping container are pulled back towards the operator. The machine appears to operate normally going forward, but stalls out and kills the engine when I try to reverse by pulling back on the operating levers.

It appears to have adequate hydraulic fluid although the marks on the dipstick and the sight tube seem inconsistent with each other. When I added hydraulic oil to get the oil level between the marks on the dipstick, the sight gauge then looked over full. Going into reverse still stalls and kills the engine.

Any ideas what I should check next?

 

[2manyrocks]

Didn't find anything specific to this kind of dumper machine, but the FB chinese mini forums seems to generally recommend changing the hydraulic oil before operating any of the mini excavators or mini skid steers. Changed out the hydraulic oil with some TSC 46 hydraulic oil. Didn't see any metal flakes or shavings on the filter so I reinstalled it. Maybe I should have washed it out first? I don't see signs that this machine has been operated much at all so I'm guessing it doesn't matter at this point.

The other usual suspect mentioned in the FB forums appears to be the control valves themselves and/or the pressure setting on them. Upon closer inspection, it looks like the nuts on the pressure settings have been rounded over as if someone already tried to make an adjustment. They were so tight that I left them alone.

Running the machine again, the hydraulic cylinders seem to run smoother now. The machine will also go into reverse if I treat the levers like on/off switches and don't try to feather them. Feathering will still stall the machine, but instantly going into full reverse seems to now work.

 

[oldnslo]

The pictures show a double gear pump. I suspect one pump feeds left track and other feeds right track. Is this correct?

Would suspect that while trying to feather the track drive the valves are restricting flow to the point of reaching close to system relief pressure but that is something you would need to check with pressure gauge.

what other function does each valve stack control? Does running the other function on both valves simultaneously stall or strain the engine?

My guess is that you need to check the system pressure on each pump section. Suspect they both should be the same pressure and may require adjustment

 

[2manyrocks]

One pump feeds the L track and the other feeds the R track. The valve stack on the left as you are standing on the operator platform controls the L track and the dumper tub cylinder. The valve stack on the right controls the R track and the front bucket cylinder.

I haven't tried to run both the tub and bucket cylinders at the same time.

When I first tried to lift the front bucket at the auction yard to load the machine, it would completely stall and kill the engine, but it is now running smoothly after changing the hydraulic oil provided that I don't try to feather the valves.

I don't have a hydraulic pressure tester, have never worked with one, and don't know how to connect one to this system. I'm not knowledgeable about working with hydraulic systems.

 

[oldnslo]

Are there any marking on the the blocks bolted to side frame that I believe are labeled LTR and RTR which i presume is left track and right track. It looks like there is valve sticking out one end but can't see the back side. These could be some form of pressure control for the track motors or possibly counterbalance to prevent machine from running away when driven on a slope.

If you don't have any pressure gauge please do not just start turning adjustments to see what happens.. You may not like what happens if you split a pump from over pressure.

If this was mine I would put a tee in the line from pump to the valves so could watch pressure as operate different functions. Determining what type of fittings were used could be a challenge.

Other challenge may be determining what the system pressure should be set at. I can see what looks like PGP *** on the end of the pump. If you can read that model code we might be able to determine displacement and then try and calculate flows to calculate pressure based on engine HP. AKA a little reverse engineering...

 

[2manyrocks]

Both the L and R tracks seem to be operating at the same forward speed. I wouldn't want to try to change the pressure settings that would cause the machine to veer to the left or right because of me not knowing what I'm doing.

The pump markings are clear. PGP5133G92 20MPa 4000r/min 2208.

The engine is a 6.5hp Briggs.

The markings on the blocks that feed the track motors appear to have a brand name "Shanyan" with a block connection diagram of C2 C1 V2 V1 and another stamping "VRDL-G3/8" 07/22. The photos on the blocks have been inverted to make it easier to read what is printed on them. They are actually upside down on the machine.

I was curious about the purpose of the blocks. What do you think they are used for?

And thank you for your help.

 

[oldnslo]

2manyrocks,
In that picture of the block for track motors the schematic on the side of the block shows being dual pilot operated check valves C1 & C2 should connect to the motor. Have you driven it down a hill? Curious how it will respond with those po checks in the drive circuit.

I tried a couple of searches and could find nothing on that pump. PGP is a Parker pump series but it is not close to a Parker model code. Doing a little math 3 HP would provide 2 GPM at approximately 2250 PSI

Does either track allow feathering in reverse? If yes does it seem like engine is straining more vs going similar speed forward? Just wondering if something is not piloting one of the checks open in reverse. You might be able to see the hose to the check swell or stiffen if this is happening.

If you are really lucky you might also be able to notice if one or both hoses to the motor are swelling or stiffening while trying to feather the directional valve.

These are non-invasive tests which is my first choice for initial diagnosis since every time you open a line you potentially introduce dirt and or create a leak.