2640 selective control valve oring question

cowman79

Member
I am still in the process of rebuilding my scv. In the parts diagram their are no orings shown in the top groove of the spool piece. Directly below the roller. On two of my spool their were orings and 2 there weren't. I am confused as to whether orings go in the groove or do not. I found a couple other parts not assembled by the book and want to make sure these are correct.
 
No o-rings on the tops of the return poppet valves, and be sure you put the short springs on the return
poppets, it will not go into float if they are in the wrong place..
 

Which valve is the return valve. The poppets look the same.
I noticed the different length Springs but they are probably not in the correct location. Thanks again for the information.
 
Here is a rough pic..
a232381.jpg
 
Is the sketch of a 2640 style or the older 4020 style. Also the two unmarked ports I am assuming are the ports going to the outlets on the back of the tractor.
 

Tim's sketch appears to be for late model rowcrop tractor scv.

IIRC depending on which way the rockers(key 16 or 21) are activated by moving the control handle the 1st valve roller moved by rocker will be the return valve followed by corresponding pressure valve on opposite rocker


38197.jpg
 
That won't be a good way to tell,, ,,looking down on your valve with the rounded part of the housing to your
left would match the sketch I made..
 
(quoted from post at 09:53:16 07/20/16) That won't be a good way to tell,, ,,looking down on your valve with the rounded part of the housing to your
left would match the sketch I made..

OK please explain why my explanation isn't a good way to determine P/R valves.
Thanks,Jiim
 
Depending on which way you move the lever to see which one opens,, you won't know which is which, but when you
look down on them like in my very rough sketch you can go by the position and when looking from the back of
the tractor it's pressure upper right/lower left...
 
I just put them in the holding fixture the same way each time and know the position for that angle, which is
upside down from your pic..
 
Don't need to see,, I adjust them the same way as the others,, put them together, send shop air back through
the coupler and adjust the screws till it Peeps a bit then back them off a half turn..
 

Ok guys I have a couple of questions. I replaced all of the poppet valves and reassembled the valve and installed back on the tractor. I am thinking that maybe I have a cam put in backwards or something. I had the control valve hooked up to a bush hog with one hose. When I moved the control valve backwards to raise the bush hog it raised but wouldn't come back down until i pushed the valve farther back to the float position. Then I swapped the bush hog to the other port and it acted very erratic. when I bench tested with air the valve opened and closed normally and I had no air coming out of the ports on the valve when in the center position. There was a very small amount of air coming from inside of the valve. I could only hear this when the top was removed. Any guidance would be appreciated.
 

I adjusted with air using the reccomendations of someone on the site. I adjusted till air started coming out and then backed off one turn and locked down the Allen bolts on the cams.
 

My guess is you possibly have pressure & return valves incorrectly identified or adjusted. Did you have rocker plates loosened during adjustment & then re-tightened the screws?
 
yes I had the side Allen screws loose during adjustment and tightened after adjustment. It seemed like on one port that the return valve wasn't opening to release pressure properly. Is there a balancing valve of any kind that would explain the small amount of air escaping from inside of the valve. This was only noticeable when I has the top removed for adjustment.
 

It's been many yrs since I supervised the scv valve adjustment. Maybe one of the REAL JD tech's will reply. Leaking air inside housing indicates leaking poppet valve to me.
 
(quoted from post at 10:10:06 07/27/16)
It's been many yrs since I supervised the scv valve adjustment. Maybe one of the REAL JD tech's will reply. Leaking air inside housing indicates leaking poppet valve to me.

During the rebuild process I had more air leaking and I found a bad poppet valve. I replaced all of the poppet valves and the air leak went to a very minimal amount of flow and nothing coming out of the ports. Where as before I had air leaking out of the ports. I am leaning towards an adjustment issue on my part I just hate that it is installed on the tractor. But we live and learn.
 

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