Stump grinder hydraulics

[bobcatbrian]

I have an SGX60 stump grinder. I bought it used in november of 09. When i bought it i noticed when i let it sit for awhile all the hydo cylinders (3) developed play. I replaced the seals in two of them but it did not make a difference. I know there should not be play in the cylinder. By play i mean i can move the rod in and out a good half inch. I am wondering if there is something wrong in the control valve on the grinder. The cylinder that raises and lowers the boom and and the cylinder that moves the head in and out are the worst, they take most of the beating and vibration. I also replaced the bushings on the main swing post and welded up the the yolks for the cylinder pins. I think because it was a rental it got the crap beat out of it. Any suggestions? Thanks

 

[frogfarmer]

They play is from air intrusion. I would expect this is normal on a well used piece of equipment. Cycling the cylinders a full stroke both ways when you go to use it should eliminate the air. As always the problem could be mechanical failure in the cylinders but I doubt it.

 

[Tazza]

They play is from air intrusion. I would expect this is normal on a well used piece of equipment. Cycling the cylinders a full stroke both ways when you go to use it should eliminate the air. As always the problem could be mechanical failure in the cylinders but I doubt it.

My thoughts too. If it had play when operating that would be different, but if its only when its been sitting, its just air, don't be too concerned.

 

[bobcatbrian]

My thoughts too. If it had play when operating that would be different, but if its only when its been sitting, its just air, don't be too concerned.

Yes by cycling the cylinders it does take care of the air until the next time i shut it down. After about a half hour its the same thing. The reason im asking is because is has started to do it while im grinding. I was grinding last week and the wheel caught the stump and basically "walked" over the stump. The cylinder that controls the in and out of the head acted like it wasnt even hooked up. It just extended all the way out. There seems to be alot of play in the cylinders when grinding and its not the pins. I am wondering if there is anything in the control valve that can be replaced to eliminate this. Other that the seals in the cylinders, which i have replaced, there is nothing to fix there and they should not have any play when the lines are pressurized. It just seems there is alot of excess vibration because of this air problem.

 

[Tazza]

Yes by cycling the cylinders it does take care of the air until the next time i shut it down. After about a half hour its the same thing. The reason im asking is because is has started to do it while im grinding. I was grinding last week and the wheel caught the stump and basically "walked" over the stump. The cylinder that controls the in and out of the head acted like it wasnt even hooked up. It just extended all the way out. There seems to be alot of play in the cylinders when grinding and its not the pins. I am wondering if there is anything in the control valve that can be replaced to eliminate this. Other that the seals in the cylinders, which i have replaced, there is nothing to fix there and they should not have any play when the lines are pressurized. It just seems there is alot of excess vibration because of this air problem.

Very weird. You said you replaced the seals so obviously the piston is tight on the end of the rod, this can cause it to move if they are not tight.
Its possible the load checks are not working as they should in the control block. They will be hidden behind plugs on the control block. I assume its an electric over hydraulic diverter, so i'm not sure how they are arranged as opposed to manual ones.
It shouldn't do it when there is pressure in the lines, something is not right there.

 

[bobcatbrian]

Very weird. You said you replaced the seals so obviously the piston is tight on the end of the rod, this can cause it to move if they are not tight.
Its possible the load checks are not working as they should in the control block. They will be hidden behind plugs on the control block. I assume its an electric over hydraulic diverter, so i'm not sure how they are arranged as opposed to manual ones.
It shouldn't do it when there is pressure in the lines, something is not right there.

Yeah, i dont think its a piston problem. Its got to be in the valve body. Like you said the check valves or something. Sounds like a good winter project for the dealer. Ill try limp it along to get me through.

 

[Fishfiles]

Yeah, i dont think its a piston problem. Its got to be in the valve body. Like you said the check valves or something. Sounds like a good winter project for the dealer. Ill try limp it along to get me through.

it could be that the nut which holds the piston to the rod is loose or the seal on the piston is leaking

 

[bobcatbrian]

it could be that the nut which holds the piston to the rod is loose or the seal on the piston is leaking

i checked the nut and it was tight, and i put new seals in

 

[skidsteer.ca]

i checked the nut and it was tight, and i put new seals in

Did the barrel look good?
You need to look up the hydraulic testing procedures in the manuals thread and test to see if the leak is in the cylinder or the valve. 1st step is to isolate the components to see whick one is causing the trouble, then try to repair it.
Ken

 

[Fishfiles]

Did the barrel look good?
You need to look up the hydraulic testing procedures in the manuals thread and test to see if the leak is in the cylinder or the valve. 1st step is to isolate the components to see whick one is causing the trouble, then try to repair it.
Ken

some cyclinders use a oring on the shaft which goes thru the piston and some don't , maybe the oil is leaking thru the the inside of the piston bore that slides over the chrome rod , I can't remember if those cylinders had that oring or not -------- I rebuilt all three cylinders on a stump grinder a few months back and got to use it to take out a bunch of stumps I had in the yard and it made fast work of it , no more than an hour to do about 12 of them in the 16 to 8 inch range , very nice attachment ---------------one way to test the seal on the piston is to remove both hoses from the cylinder and cap off the fittings and see if you can push the cylinder in or pull it out while it is capped or to make a fitting that will adapt to the fitting on the cylinder and hook it to an air supply and try and push air thru it or dead head the cylinder in one direction then take off and cap the out side of the way you are moving the cylinder , with the fitting on the out side opened apply pressure to the inside and see if oil is making it by the piston seal ---------maybe the controll valve spool is not centering due to corrision in the spring cap

 

[frogfarmer]

some cyclinders use a oring on the shaft which goes thru the piston and some don't , maybe the oil is leaking thru the the inside of the piston bore that slides over the chrome rod , I can't remember if those cylinders had that oring or not -------- I rebuilt all three cylinders on a stump grinder a few months back and got to use it to take out a bunch of stumps I had in the yard and it made fast work of it , no more than an hour to do about 12 of them in the 16 to 8 inch range , very nice attachment ---------------one way to test the seal on the piston is to remove both hoses from the cylinder and cap off the fittings and see if you can push the cylinder in or pull it out while it is capped or to make a fitting that will adapt to the fitting on the cylinder and hook it to an air supply and try and push air thru it or dead head the cylinder in one direction then take off and cap the out side of the way you are moving the cylinder , with the fitting on the out side opened apply pressure to the inside and see if oil is making it by the piston seal ---------maybe the controll valve spool is not centering due to corrision in the spring cap

Do you ever notice a problem with the hyd oil foaming? A flow restricter can cause the oil to foam under certain conditions. Most implements like stump grinders have flow control built in to the valving so the head doesn't jump all over the place. Some valves are setup to maintain back pressure on the system to help avoid the problem you are experiencing. Cavatation in the drive motor of the cutting head could cause air. Just a thought but still sounds like air; problem is where did it come from.