420C hydraulic spool valve

[Cubby267]

Reaching out to all those with expertise on hydraulic systems on the 420C. I have purchased a 420C which came with 2 blades, an outside mount straight 6' and a hydraulic power angle inside mount 6' blade. The straight blade is currently on the crawler and I am investigating what I need to install the angle blade. While I think I have all the mounting hardware I am confused on the hydraulics. The angle blade uses 1 lift cylinder and 1 angle cylinder. I did get both cylinders but I also got a 2 spool valve that is identical to the spool valve that is on my crawler now (tank mount). I don't understand how that spool valve can run both cylinders independently? Am I incorrect in thinking that the valve on my crawler is 2 spools both single acting? My thought right now is to stack the 2 spools from my spare valve onto my current valve for 4 spools and add a handle to run 2 cylinders independently?
If someone can show me the error of my thought process I would appreciate it. Maybe easier, I could by a 2 spool double acting joystick and put it on the fender. I would like to stay with the original tank mount spool valves if possible.
One more question for the group, is there a commercial seal kit for the spools valve or do I need to reach out to Lavoy?

Thanks for any help.

[Jim B]

The original set up used two single acting spools to perform the work of one double acting spool. This was accomplished through the linkage that controlled the spools and even allowed for a "float" position.

I believe you would need to restack your valve with spool sections from the second valve to make a 4-spool valve with a handle for each of the two spools as they are currently operated (the parts catalog (PC505) for the 420 shows a 4-spool valve bank arrangement. If you are going to do this, you may be best served by using a new two spool control valve for double acting cylinders, if your valves are worn and leaking internally around the spools. A loader valve with a detent float position would be best for a dozer, so you could retain a float for the dozer lift circuit. Flow rating should not be a problem if you are using the OEM pump (driven from the engine cam). You will need to watch to see that the pressure relief valve can be set low enough to match the OEM spec. Trying to jack the pressure up on the OEM pump can destroy it.

Check with Lavoy on seals for your valves. I don't think JD has a complete kit for them (I expect you will need to order as individual parts), however Lavoy may be able to put something together for you. I believe the only seals are O-rings of quad type rings, used externally. The internal sealing of spools to valve body is by clearance, not seals. There are seals between the valve body sections as I noted above.

[420C-Mike]

Jim is correct in regards to restacking the valves. Theoretically the double remote assembly uses a different end cover without the return port but this can most likely be plugged and reused.

I am on a "long term" overhaul of my 1956 420c ( I can now drive it around after I finally got the the tracks that Lavoy rebushed and pinned a few years ago back on) and am adding a 3 point so I have a similar need for a double remote valve. Over the past couple years I have collected from various sources 2 additional single remote assemblies as well as the correct end plate, and a second handle to assemble a double remote "original" valve stack. My challenge is the shorter control rods.

DOES ANYONE HAVE A SOURCE, DIMENSIONAL SAMPLE OR SPECS OF THE SHORT RODS P/N AM2951T? I plan to check with Lavoy as well. My next step however will be to remove and rebuild the hydraulic pump as it has stopped working.

A never ending but very enjoyable project!!
Mike

[Jim B]

The leaks and wear in the old valves and linkages along with the difficulties you are having finding parts to modify your valve are why I say a new two pool loader valve with float is a better answer, unless one is trying to do a period correct restoration, to me.

[Lavoy]

To add to what Jim has said, if you are not concerned about being orginal, then a new aftermarket valve is a great way to go. Just make sure to get a low pressure valve that will go down to 1000PSI. If you run the cam pump at high pressure, you will just blow the pump. Also make sure to set the valve pressure with a gauge once installed, even the low pressure valve are usually set at 1500PSI.
Lavoy

[Cubby267]

Thanks to all for the knowledge and advice. I need to re-seal my current spool valve (leaking at the detent pin cap). Spool valves themself looks OK with no leakage. Dealer had in stock the seals (O-rings)for the detent cap. Since I have the spare valve I think I will go ahead and do the 4 spool stack with the additional handle. If I don't use the angle blade I could have a remote set at the rear. Guess I need to start the search for the OEM second handle.