Back hoe for Jinma very jerky in movements: Chinese Tractors -- Jinma Farmpro Agracat  -- Chinese Tractors Discussion Forum and Review Back hoe for Jinma very jerky in movements: Chinese Tractors -- Jinma Farmpro Agracat -- Chinese Tractors Discussion Forum

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Discussion Boards > Active Subjects > Messages as Posted > Chinese Tractors -- Jinma Farmpro Agracat Forum

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 06-15-2006, 07:57 Post: 130884
locksleyred



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 Back hoe for Jinma very jerky in movements

I have a JM354 and a 3 point linkage B'hoe. I have had problems with the oil frothing out but that seems to be solved for now. Thanks to all those that have helped out. However, now that the B'hoe is operational I notice that it is very jerky in its movements no matter how hard I try to be gental with the control levers. I took the valve cover off and noticed that I could not adjust the oil flow into the valves at all there is just no adjustment available.
Is there an add on I can put on to slow the oil to make for more smoother operation? And where do I put it? Can I control the whole valve system with one control 'add on' or do I need to put one on every, say, inlet hose to each valve? Look forward to your suggestions.

Thanks
Mike






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 06-17-2006, 19:30 Post: 130964
earthwrks

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 Back hoe for Jinma very jerky in movements

Describe the point in time when it's jerky. For instance, let's say the b'hoe is fully extended and fully raised. When you bring or crowd the dipper stick it sort of falls or travels on it's own as it goes past center, then it stops and continues. If it does this then there could be air trapped in the cylinders which needs to be bled or the pump is either being run at too low an RPM, or the pump is too small and can't keep up, or the pump is going bad and is aerating the oil which will cause even more wear to the pump. I doubt very the problem is in the controls unless the controls (the spools inside) is sloppy inside the bores.






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 06-18-2006, 17:28 Post: 130996
locksleyred



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 Back hoe for Jinma very jerky in movements

Hi earthwrks,
Ok I can best describe it in this manner. No matter careful I am with the operation of the controls it's either full on or full off. So it very noticeable in the slew of the arm. When I go to dump the load by say swinging left the whole arm starts off quickly and when I go to stop it it stops abrubtly and the whole b'hoe sways from side to side.( not drastic but shakes 4 -5 times then stops. ie stop the slew and the hoe will bounce back 4- 5 inches decreasing until it stops) I dump the load and swing back to the trench I am digging ... I can't slow it down so that I stop over the trench. I either go too far or not far enough. So when I try to reposition the bucket over the right spot I have to move the bucket which again makes for very jerky movements. The shaking can't be good for the machine.

It's a bit like variable speed electric drills and saws as opposed to direct start ones which are either full on or off. Once you get a variable speed tool you never want to use the old style again. And besides they are safer.

I don't think its air but then again I'm not an expert in hydraulics, which then begs then question, "if it is air what is the protocol for bleeding the rams?" What you describe above does not happen.

The unit on the B'Hoe is rated to 40litres/m, I can't make out what the pumps actually says it can do and there is no documentation to tell me either. However, the slower I run the tractor revs the smoother the movements on the B'hoe. I have however, been told that I should have the tractor revs up to approx 1000 - 1200 when using the B'hoe.

The b'hoe is brand new so no slop in the controls.

I have operated other B'hoes allbeit for a few minutes and found them to be very smooth indeed. I have also looked at other forums but found nothing at the moment to help me. I'd imagine that there could be ways of making the controls run more smoothly apart from buying an after market unit at around the $AUS400 mark.
I am a person who takes all suggestions on board and look forward to any comments.

Thanks mate

Mike.






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 06-18-2006, 18:06 Post: 130998
earthwrks

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 Back hoe for Jinma very jerky in movements

Do you have a backhoe that uses two cylinders down low that sit nearly parallel to each other to slew it? Or do you have a rack-and-pinion system; or a large, 2-section roller chain connected to a sliding cylinder(s)? In either case there may be too much slop in the pivots or the bushings are worn so much that what you are seeing is sloppy tolerances. Bushings can be replaced, chains can be tightened; a rack and pinion can be harder to take the slop out of (I'm not aware of a fix for that).

Also, what I've found is the that since the backhoe is a horizontally mounted pendulum---whith some sloppiness when worn---, the plumbness of the hoe main pivot has a big bearing (no pun intended) on how the hoe stops and starts swinging or slewing. For example, with looseness like I get on mine if the hoe is perfectly level or rather the main pivot is, the hoe works predictably and smoothly. But raise the rear of the machine and the hoe swings rapidly and stops hard to one side or the other (read: crashes). Lower the rear and raise the front, and the opposite happens: the hoe swings softly from the center to the sides, but can swing hard and swiftly to the center which can make for repeatedly difficult alignment to the trench. One way to slow the slewing action and make it more mansgeable is to reduce the size of the hoses or fittings at the cylinders. This in effect reduces the amount of oil going to the cylinders slowing movement, sort of like kinking a garden hose.






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 06-19-2006, 17:53 Post: 131045
locksleyred



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 Back hoe for Jinma very jerky in movements

Hi Earthwrks,
Read your post last night. Went outside this morning to double check a few things.
The machine is brand new so I figured that all the bushes would be tight anyway, but I did double check. Using an endless chain winch I lifted the arm of the unit so that all weight was off the pins etc. Checked for sloppiness but did not find any no matter how hard I looked. Actually one pin they sent with the unit was undersize so had to buy the proper one. Your suggestion really sent me looking for other undersize pins but everything here was OK.
Ok there are 2 cylinders that operate the slew at the bottom as you said, but all tight as.
Yes that's one option of slowing the slew down is by reducing the flow of the oil to the cylinders. We have a compnay here called ENZED that deals only with hydraulics and they also suggested that, but they said that while this would work it could actually heat the oil too much. They wanted to know the flow of the pump, something I could not say and I am still waiting for the manufacturer to tell me.
It could be that the pump is pushing to much oil. Reduce this and it could reduce this jerky movement(s).
I think that the control unit is basic at best because it would appear that it is either full on or off, and coupled with a pump that could be too strong would not help the situation.
Greg's suggestion of an aftermarket 'controlable' valve unit could be the best way to go. But I will wait for the details on the pump flow before I go down that track.
Thanks again Earthwrks.

Regards

Mike






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 06-19-2006, 19:20 Post: 131048
chipuren



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 Back hoe for Jinma very jerky in movements

A characteristic of the china made backhoes is a very short taper on the control valves that make them jerky to operate. Another characteristic is their very low priceSmile






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 06-19-2006, 19:54 Post: 131049
earthwrks

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 Back hoe for Jinma very jerky in movements

Reducing the hose or fitting size at the cylinder is not going to heat the oil up since the metering is done at the the valve body, which is its purpose. And th ouild doesn't circulate --it goes to the cylinder for a second and then is forced back when you selw the other way. The oil still has to go through the spool valve, it's just that not as much volume will be needed, and you're controlling the volume and the valve. The heat build up comes from reducing the size from the pump to the valve, not from the valve to the cylinder at least not for this application.

As far as th on/off feel of the valve lever or "throw", try making the "throw" longer either by changing the geometry of the lever connection at the valve to the lever, or making the lever longer. This will give you more control. I haven't seen your valve set up, but I'm thinking a bell-crank having different length legs/sides/ended may do the trick. Your goal, based on what I know of your situation, is to take a long throw and get very little movement from it at the valve spool.

If that doesn't work you may want to consider buying a used valve bank from a bucket truck, just make sure it has the same number of levers and can be plumbed-in relatively easily.

Also, look (e-Bay is a good source) for a used valve bank from a DitchWitch, Case, or Vermeer (common in the States) ride-on backhoe trencher. A valve bank from a tree trimmer truck (A.K.A. "bucket truck" or "cherry picker" here or "lorry" down unda').

For reference, I have a 1987 Case, 4x4, ride-on, trencher and backhoe (for sale $4500 USD) that probably has the perfect valve bank set up.






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 06-20-2006, 04:58 Post: 131062
locksleyred



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 Back hoe for Jinma very jerky in movements

Point taken Chip, just to let you know there was a smile on my face when I read the last part of your post. Point is, no tractors are made in Australia anymore, the last being 40+ years ago.
So everything AG has to be bought in. Detachable backhoes are not common. I've only seen old ones and they came with the old Cranvel tractors. Yes they are cheap, its a pity they (Chinese) don't put in the hard yards to make something good ... perfect. Well, very good lets say.
Actually Earthwrks came up with a good suggestion and that is to look for a good second hand unit.

regards

Mike






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 06-20-2006, 05:23 Post: 131063
locksleyred



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 Back hoe for Jinma very jerky in movements

Hi Earthwrks.
Funny how minds think alike. All the locals decided today was the day to come and inspect my new Chinese toys. I also bought a 15Kw generator, and various motors, pumps, smaller generators, pressure washers etc for the locals as well. I basically filled the container with other peoples goods.

Well the 6 of us basically came up with exactly what you suggested even to the point of extending the lever arms to see if that would make a difference. If it did it wasn't noticible. The two levers operating 4 valves were already long anyway but we tried.
One guy even said your first paragraph almost word for word!! So I will try this first. The local hydraulic shop has a valve which can fit inline and it may do this job it's just a matter of seeing if the Chinese threads are compatable with European and American units on the market.

Your second hand unit idea is worth looking into and will do that also.

We call them Cherry pickers here as well. Lorry is basically and English term.

Just one question though, if the oil does not circulate, how do you air bleed the line/ rams etc?
Thanks mate

Mike






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 06-20-2006, 06:49 Post: 131066
earthwrks

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 Back hoe for Jinma very jerky in movements

I don't think you need an inline valve (that will need a return line to tank)---simply a smaller diameter fitting should do it.

WHen I used to write service manuals for convertible cars we recommended (in short) removing the cylinder with hoses attached, fully extending them in a vertical postion (piston rod end up) let it sit for a few minutes to allow the bubbles to settle out, crack the fitting at the rod end to let air escape, and close. Retract, and repeat until air is out. The fitting should be facing the sky too. To do the other end of the cylinder turn it over and repeat procedure, reinstall cylinders. NOW---you may get away with just cracking fitting when cylinders are fully extended or retracted, but oil can still hold bubbles if they can't escape.






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Discussion Boards > Active Subjects > Messages as Posted > Chinese Tractors -- Jinma Farmpro Agracat Forum

Thread 130884 Filter by Poster:
chipuren 1 | earthwrks 5 | locksleyred 6 |




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