TCV relief setting

[Harry]

I have had a problem for a long time on the 646.
The relief valve would open to early somewhere close to 1800 psi. I always wanted to adjust it but after crawling under the tractor there is no way to get a wrench or my hand in there. I know what the manual says, but I think the engineers just dream this up without ever attempting it. So I read a post about cutting a hole in the floor to access the adjustment. So yesterday I used my plasma cutting machine and cut a rectangular hole in the floor, making sure not to start the tractor on fire and burn the shop down. Then cleaned up the area with a grinder. The crown cap was easy to take off but the adjustment screw was more difficult to turn. Using a tool that is bent at a 90 degree angle I could turn the screw one full turn. Then made a access cover that I drilled holes to mount to floor. Marked floor for hole location, then drilled and tapped for appropriate bolts. Painted cover and bolted it on the floor this morning. Tried the tractor out this morning with tiller on and relief valve not squealing. I haven’t tested to see what pressure it’s opening up at, but I mounted a gauge in dash a while ago to check, so easy enough to do. This compact tractor is 50 years old and probably the first time the relief valve was ever adjusted. Harry

[myerslawnandgarden]

There should be a hole in the frame at the rear so that you can use a long extension to adjust the main relief valve. I can't remember for sure, but I think that the mounting plate for the 3 point hitch may cover the hole.

Bob

[Harry]

Yes that is what the manual says. You cant get the crown nut off to get a long extension on the screw, yet turn it with the extension you have to make. I had a hard time turning it through the window I cut out. Engineer pipe dream in my opinion. Harry

[MattA]

Has anyone put together a list of parts required to test the relief valve settings for both travel and lift circuits?

[DavidBarkey]

Has anyone put together a list of parts required to test the relief valve settings for both travel and lift circuits?

I have a permanently mounted pressure gauge with a 1/8" NPT hydraulic hose . The hose goes from the presser tap on the valve to the gauge .The biggest thing is bleeding the hose .

[dhitching]

Has anyone put together a list of parts required to test the relief valve settings for both travel and lift circuits?

If you have a rear PTO it's pretty straightforward. Because the PTO is the first item on the hydraulic circuit right off the pump, you can put a gauge inline and see the pressure when you trigger the lift relief or the travel relief. You can also use a ball valve to test the PTO relief, closing the valve slowly until the relief valve on the PTO is squealing.

Note that on any tractor with a dual pump setup this will only check items on the travel circuit. So on a 6018 or 4120 you can't check the steering or loader relief via the PTO.

[MattA]

Has anyone put together a list of parts required to test the relief valve settings for both travel and lift circuits?

If you have a rear PTO it's pretty straightforward. Because the PTO is the first item on the hydraulic circuit right off the pump, you can put a gauge inline and see the pressure when you trigger the lift relief or the travel relief. You can also use a ball valve to test the PTO relief, closing the valve slowly until the relief valve on the PTO is squealing.

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Note that on any tractor with a dual pump setup this will only check items on the travel circuit. So on a 6018 or 4120 you can't check the steering or loader relief via the PTO.

Thanks for posting. That's a lot easier than I thought.

[Harry]

I used the 646 with tiller to prepare a nursery area for next year. Area is 30’ X 30’ which I back filled with dirt that I dug out with 644 lbh. Since increasing pressure the tractor never squealed the relief valve and never got stuck. It was like a new tractor, what a beast to drive and till with. I was wondering at what pressure the relief would open at. So before putting the tractor away I drove it up to a dumpster that is currently in front of my shop. It opened at 2800 psi. when pushing against the dumpster. I still have a few items to look at and it’s supposed to to rain this weekend.

[MattA]

Sounds like a beast now Harry.

Hydraulic test procedure with relief settings is attached.

Hopefully Harry doesn't mind me asking here, does anyone know if the later 4 digit tractors with the backhoe transaxle had the standard 2100PSI relief or if they were increased to 2400PSI like the loaders.

[dhitching]

Does anyone know if the later 4 digit tractors with the backhoe transaxle had the standard 2100PSI relief or if they were increased to 2400PSI like the loaders.

The 4 digit backhoes followed the loaders from 2100 -> 2400 -> 2750 -> 3000 over the years. It should be noted that the later 4 digit backhoes got 3000psi rated Eaton pumps instead of the 2500psi rated Parker HD pumps the loaders and early 4 digit backhoes got.