Cockshutt 1855 Hydraulic Problems

Hello everyone, I have a 1855 Cockshutt that I cant seem to get to run. The engine was rebuilt a while ago and the tractor and engine have since been sitting unused. The tractor was bought in a non-working order and it was said the engine was not running, I do not have a lot of information on the tractor at point of purchase but as of then the engine was rebuilt and is running alone. As i started hooking up the engine back to the tractor i noticed when the long pto shaft was inserted into the housing->flywheel the engine would no longer run. This seems to be do to the shaft engaging the hydraulic pump.

The oil is full, the pump pumps. As the pump builds pressure there is a hydraulic lock somewhere which eventually stalls the engine. The engine will run for only a short few seconds and then stall. I have changed the oil and filter and through some trouble shooting have determined that it is indeed a hydraulic lock problem because I can disconnect any high pressure line and the engine will continue to run as the disconnected line relieves the pressure(the line goes into a bucket, there is good flow on the pump). I am leaning towards a pressure valve being stuck closed or perhaps the return line wherever that may be is plugged solid.


I'm not sure where to look next as i don't know exactly where the return lines are suppose to be, the three valves located in front of the pump/filter on the side of the tractor have been taken apart and cleaned no apparent defects or foreign matter. There does seem to be lines going everywhere from the valves tho, im not sure if it is the original plumbing as i cant understand why the high pressure valve would loop back to the high pressure valve relief outlet.

The valve path is like this
HPV---> (T's off too..)Power steering/Unloading valve--->Unloading valve T's to 3 pth and a return line back to the return on top of the high pressure valve.

Does anyone know if the pump itself is suppose to return oil into the transmission housing if the pressure locks. 3pth and power steering work until the engine stall. turning the steering seems to prolong stalling as it relieves pressure. also if i loosen the high pressure relief valve so that it is about half way out the tractor will run but i do not enough pressure in my hydraulics for the steering or 3pth to operate. This really boggles my mind as i said before it appears the pressure relief valve is looped so i don't understand why loosening the valve would stop the hydraulic lock and let the engine run.

Any comments would be greatly appreciated.

Thanks,

Nathan

Did you check the compensator pressure and the pressure of the relief valve? You know that is a closed center system? You have e-mail?

Hello Schwiebert, my email is [email protected]. I have sense taken apart the compensator valve and pump cover (valve plate) because the compensator valve cap on the other side fell off so i figured i might as well take a look i didnt seem to find anything there. I left the valve loose and tried the engine. the engine ran while the valve was loose. i found as i tighten it again it would stall. if i have the valve somewhere inbetween it seems that when hydraulic oil is used ex steering or 3pth it seems to stall but before it would actually seem to stop the engine from stalling. i noticed there is some type of click noise after the pressure dissipates ( you can see the lines shake as the lock up around the valves) in one of the valves. so i took the valve housing off again and had a second look. i noticed in the pressure reducing valve there seems to be a secondary relief valve that calls for a shim and in my case it had 4 so i took 3 out, part #29 in agco parts book page 151. everything else is identical to this parts blow-up. i reinstalled and tried again with all valves tight including compensator(was marked or locked from factory & returned to that turn) as it was before and again no change. still am not 100% where exactly excess oil pressure is suppose to relieve and to where or how many i do believe there is one small line top side of pump for return. is it possible something is jammed in a line inside the transmission somewhere. although the valves and pump ext where very clean and shinny with no debris. the original oil that i drained was dark especially near the bottom of the trans but didnt seem to have clumps or any metal.

Also i do not have a oil pressure tester, but there is pressure through the pump and valves as i had the 3pth and steering working.