Bobcat 331 Excavator Hydraulic Thumb problems

   / Bobcat 331 Excavator Hydraulic Thumb problems #11  
Correct. The check will prevent oil going into your new valve from the rod side when opening is commanded.:thumbsup:
 
   / Bobcat 331 Excavator Hydraulic Thumb problems #12  
Jabonee is correct that there is not a port relief in that auxiliary valve section, but there a simple port relief installation for this. Below is quick photo snip taken from the Installation Instructions for a Bobcat Thumb. For this serial number order Port Relief part number 6680065 and install it in place of the anti-cavitation plug the is in valve now.

View attachment 447707

You got my brain smoking a little SSDOXIE. Service and parts don't seem to jive. JIC schematic shows port reliefs for AUX valve. Disassemble and reassemble in the service Manuel do not. I found the pt# you posted. I'ts listed as a port relief for the extendable arm. No value listed but I'm sure its fixed.This may be the easier solution but it may require removing or disassembling the AUX valve to install it.
 
   / Bobcat 331 Excavator Hydraulic Thumb problems #13  
No disassembly of valve required. Just remove the plug cap currently in valve and install. If he has the hoses connected to correct coupler on the boom, the this plug goes in the top side of the valve as it sets in the machine.
It is shown in the installation instructions for the clamp (thumb) Bobcat sells for that machine. Here is clip from next page of instruction, shows better where it goes.
331 thumb port relief,pg2.JPG

The only 331 models that did not have provision in the valve for port relief were very early models; all those with 5519 as first 4 digits of serial number and 521913973 and below. All others will accept simple port relief installation in not already factory equipped.
 
   / Bobcat 331 Excavator Hydraulic Thumb problems
  • Thread Starter
#14  
No disassembly of valve required. Just remove the plug cap currently in valve and install. If he has the hoses connected to correct coupler on the boom, the this plug goes in the top side of the valve as it sets in the machine.
It is shown in the installation instructions for the clamp (thumb) Bobcat sells for that machine. Here is clip from next page of instruction, shows better where it goes.
View attachment 447778

The only 331 models that did not have provision in the valve for port relief were very early models; all those with 5519 as first 4 digits of serial number and 521913973 and below. All others will accept simple port relief installation in not already factory equipped.

Is it adjustable or is it already set to the correct pressure to be overcome by the bucket. So, it's as easy as basically removing the existing plug with the part # you provided? You had me scared on the 1st post as it did look like I was going to have to remove the valve assembly!!

Update: Just went and looked and can't seem to find any plug per say. This is what I have, which is close, but doesn't look like the pic where it looks like plugs are on the top.

IMG_20151121_090025.jpg
 
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   / Bobcat 331 Excavator Hydraulic Thumb problems #15  
Not sure if it is adjustable or not, I think it is. Your current problem is not what relief pressure is, but that there is no relief at all when the auxiliary (thumb) control is in neutral. The fluid is locked in the cylinder so when the bucket pushes against it the weakest point is the extended cylinder rod which bends.

The last photo I posted shows a port reliefs in the valve sections just to the right of auxiliary, these appear to have jam nuts on top of the cap so are adjustable. Part number for the Auxiliary relief is same as the port relief for the dipper arm cylinder which is second to right of auxiliary valve.
 
   / Bobcat 331 Excavator Hydraulic Thumb problems
  • Thread Starter
#16  
Not sure if it is adjustable or not, I think it is. Your current problem is not what relief pressure is, but that there is no relief at all when the auxiliary (thumb) control is in neutral. The fluid is locked in the cylinder so when the bucket pushes against it the weakest point is the extended cylinder rod which bends.

The last photo I posted shows a port reliefs in the valve sections just to the right of auxiliary, these appear to have jam nuts on top of the cap so are adjustable. Part number for the Auxiliary relief is same as the port relief for the dipper arm cylinder which is second to right of auxiliary valve.

Take a look at the pic I posted.....I don't see anything that resembles jamb nuts on caps.....do i have too early a SN to use that part#? Sorry for the ignorance and I surely appreciate the help!!
 
   / Bobcat 331 Excavator Hydraulic Thumb problems #17  
OK, a little more research on my part. The port reliefs on your valve are located behind the spool caps (with the small hydraulic lines) and recessed in the valve casting, end cap does not stick above the valve casting. The part number I gave is correct and is preset to 2950 psi.
 
   / Bobcat 331 Excavator Hydraulic Thumb problems
  • Thread Starter
#18  
Sweet!! Good info, and I surely appreciate it!!
 
   / Bobcat 331 Excavator Hydraulic Thumb problems
  • Thread Starter
#19  
OK, a little more research on my part. The port reliefs on your valve are located behind the spool caps (with the small hydraulic lines) and recessed in the valve casting, end cap does not stick above the valve casting. The part number I gave is correct and is preset to 2950 psi.

So I looked where you described and found what seems to be an adjustable piece rather than just a plug. Of course I'm assuming it is adjustable just due to what seems to be a set screw type on top. Any thoughts?IMG_20151122_122354.jpg
 
   / Bobcat 331 Excavator Hydraulic Thumb problems #20  
Looks correct. I wonder if it has a mate on the bottom side?
 
 
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