BH65 Thumb Conversion Help

[J0be269]

Forgive me please if there is a simple answer to this, but I need some help from the experts.

I am in the process of converting the mechanical thumb on my Kubota BH65 Backhoe(mounted on a Kubota B2620) to hydraulic operation. I have the cylinder mounted and all lines ran, but the cylinder will not move.

Here is the valve I used.

The first attempt was as follows.

I plumbed the pressure line from the tractor (I Think......it has a male QD on the tractor side that a female from the hoe hooks into) to the pressure port on my new valve. PB from new valve to BH valve, and Tee the new valve tank port to what I Think is the BH return line. (It has a male QD on the hoe that a hose from the tractor hooks into)

The first attempt resulted in the hoe functioning correctly until the new valve is actuated, at which point the new cylinder would move slightly then the hoe boom would start to drop.

The Second attempt was as follows.

I plumbed the tractor hydraulics pressure line to the BH as usual (I think it's the pressure line, has male QD on tractor side that BH hose connects to) I then plumbed the BH return line (I think....it has male QD on hoe that tractor female hose hooks to) to the new valve pressure port. Converted valve to open center and ran new valve tank line to where the BH tank line (I think.....we're still going to that male QD on the hoe here).

This resulted in normal hoe operation, thumb reacted the same as before.....but no hoe droop this time, instead the relief kicked in.

Note that I only activated the new valve momentarily each time so as to reduce risk of damage.

Is it possible that I just have what I THINK is the tractors pressure and return line mixed up? Note that these hoses hook to each other when the hoe is not on the machine. When the hoe is mounted the three point hitch valve must me locked in the lower position.

Please help, I have no hair left to pull out.

 

[J0be269]

Well I feel like a moron.....I answered my own question while writing the question. I was able to get time to go back and look at it again, and I did have the pressure and tank lines from the tractor mixed up. This thread can be deleted or it can stay so others can learn from my mistake. For anyone curious I will do a write up of the whole project in the projects forum once I get my linkage in place. :thumbsup:

 

[wdchyd]

Well I feel like a moron..... :thumbsup:

Better to feel like a "More On" than need a good "Less On"......

That's why they make erasers on the end of pencils......

 

[CHDinCT]

Despite your false start (that's why they invented the Mulligan) it sounds like a cool project I'd love to see more details and pic's on. Post a link to your project thread why you get a chance.

 

[Ductape]

Ummmmm ............... yeah, I agree. We need plenty of pics of this.

 

[numerobis]

i had the same problem with mine.. i used the same valve body as you...
i put a power beyond into it... placed before the backhoe valve body... i also plumbed a 3rd return line for the thumb cylinder
and ajusted the line releif a little lower than the bucket this way if i close the bucket the thumb retract


here is a few pictures of my hydraulic full rotation thumb on this pictures it is not finished...


i made myself also a quick coupler...

 

[Luremaker]

i had the same problem with mine.. i used the same valve body as you...
i put a power beyond into it... placed before the backhoe valve body... i also plumbed a 3rd return line for the thumb cylinder
and ajusted the line releif a little lower than the bucket this way if i close the bucket the thumb retract


here is a few pictures of my hydraulic full rotation thumb on this pictures it is not finished...
View attachment 297464View attachment 297465View attachment 297466

i made myself also a quick coupler...

Welcome to TBN. Can you expand on how you plumbed in your valve for your thumb.

 

[numerobis]

here is a basic ms paint shematic hope this will help...

this valve body is mounted in serial before the bh65 valve body
a power beyond needs to be installed.. to avoid pressure buildup in the thumb valve body by operating the backhoe
an aditionnal drain line for the thumb needs to be installed otherwise your thumb will not work properly

 

[J_J]

If you install the thumb valve before the BH valve, you will limit the BH pressure to the pressure that is set on the thumb valve relief valve.

I think you should install the thumb valve after the BH valve.

You want the BH bucket to always override the thumb , you will need to figure the relief pressure for the thumb valve to relieve.

Depending on the size of cyl and mechanical setup, you will have to figure out the relief pressure to allow the thumb to recede when the bucket force is greater.

All return/out lines should go to tank.

The BH relief valve should be set the same as the tractor relief valve.

 

[numerobis]

if i install the thumb after the backhoe if i do any action on the backhoe the thumb wouldnt work no more because there is a parrallel feeder into the bh65 valve body


normally the Actions Releif on en excavator are generally higher than the main releif.... thats mainly because the line releif are not full flow the main releif is full flow