M-620 valve block.

[Kilroy2k1]

You guys were excellent in sorting out my hydrostat problem so now its time to tackle the next item on the list of todo's, the valve block.
The machine is useable but there is definately some internal leaking going on in the valves, the lift and tilt both sink a little faster then I am comfy with. The biggest problem I hope to solve is the lift arms have an insanely fast drop, as if you disconnected the hoses, should there be some sort of regulator or restrictor for that or is this normal for such an old machine? Another minor issue is the float dosent seem to work, it maintains downward pressure when you press it into detent.
Any ideas or things I should look out for when pulling this thing apart?
Tom.

 

[mllud]

The load checks are what hold the position . I think they should be accesable without pulling the whole valve block. The parts may not be available without buying a whole kit. It may be better to rebuild the whole unit.
The Bobcat guys will know more than I do on your unit. Your making good progress. Some people let a few minor repairs go and operate an unsafe machine. Mike

 

[skidsteer.ca]

Likely the piston seals on one or both of your lift cylinders is leaking past, or it can be the control valve the foot pedal attaches too.
You can pressure test the seals on the cylinder piston with compressed air and see if they are sealed or bypassing the piston and escaping out the opposite port on the barrel.
If the pistons are sealing. then hook a 3000 psi pressure guage to the hose that goes to the back end of the cylinder and plug the hose going to the opposite side of the machine on the back end of that cylinder.
Start the machine and push the pedal to lift the boom. The guage pressure should rise (the boom should not lift if you hooked into the right hose and plugged the other one) to about 2250 to 2500 psi and stay near there when you release the pedal. If the pressure drops back down to 0 you have a problemwith a nternal leak in the control valve or a bad hose. (the hose is unlikely because you would notice the oil leaking out everywhere)
Ken

 

[Kilroy2k1]

Likely the piston seals on one or both of your lift cylinders is leaking past, or it can be the control valve the foot pedal attaches too.
You can pressure test the seals on the cylinder piston with compressed air and see if they are sealed or bypassing the piston and escaping out the opposite port on the barrel.
If the pistons are sealing. then hook a 3000 psi pressure guage to the hose that goes to the back end of the cylinder and plug the hose going to the opposite side of the machine on the back end of that cylinder.
Start the machine and push the pedal to lift the boom. The guage pressure should rise (the boom should not lift if you hooked into the right hose and plugged the other one) to about 2250 to 2500 psi and stay near there when you release the pedal. If the pressure drops back down to 0 you have a problemwith a nternal leak in the control valve or a bad hose. (the hose is unlikely because you would notice the oil leaking out everywhere)
Ken

The machine is already apart but I can lift the arms and put a ball valve between the lines to test holding. I'm 100% sure the block is leaking internally as well because the previous owner changed all the cylinder seals for the same reason and the issue never improved. The block has some minor external leaks around the spools so I might as well do the whole shot at once. Initial purchase price was very reasonable and I know the last 15 years of its history so it does not hurt too much to put some good money into this unit.
Tom.

 

[Tazza]

The machine is already apart but I can lift the arms and put a ball valve between the lines to test holding. I'm 100% sure the block is leaking internally as well because the previous owner changed all the cylinder seals for the same reason and the issue never improved. The block has some minor external leaks around the spools so I might as well do the whole shot at once. Initial purchase price was very reasonable and I know the last 15 years of its history so it does not hurt too much to put some good money into this unit.
Tom.

If the rams have been done it will have to be the load checks, remove them and look for shredded seals, i had a 731 that was really bad. Replaced the seals and it was perfect!

 

[Kilroy2k1]

If the rams have been done it will have to be the load checks, remove them and look for shredded seals, i had a 731 that was really bad. Replaced the seals and it was perfect!

I pulled the block apart and none of the seals appear damaged, but they are definately old and stiff so they may have been leaking. the load check poppets are a metal on metal seal so I'll have to devise some way of lapping them to be sure of a good seal there. I'm happy to see the spools are in good shape, some micro scratches but nothing to be concerned about. Once this block is done and everything is back together I can do a proper pressure test and see if the relief spring is as tired as the checkvalve spring was.
Tom.