I got a service manual for my machine and was looking through it. I am going to be installing a hydrualic thumb and will want to make sure the pressure relief is set right. I didnt see anything about it in the manual. Has anyone done this before? Machine is a 2004 komatsu pc78mr-6
I just got a IHI 35n2. It had a aftermarket hydraulic thumb on it. I am also searching on how to adjust releif pressure on thumb as I have broke thumb cyl rod with curl bucket. I just joined this as this is my first post. If pressure is not adjusted rifgt it will cause problems. But you will enjoy the thumb.
The way I check circuit relieve pressures is I use a hand pump to pressure up the work port from the cylinder side of things. But if you don't have one you can just follow you thumb cylinders base end hose back to the main control valve. Where this hose connects to the valve there should be an adjustable relieve inline with that work port. Loosen the lock nut and unscrew the set screw a quarter turn, tighten the lock nut back up. Start the machine and close the thumb against the bucket. Curl the bucket in and see if it will over come the thumb. If it doesent go back to the circuit reliefe and give it another quarter turn out. Try the bucket thing again, keep doing this until the bucket just over comes the thumb cylinder. Hope this helps.
I have followed the lines back to the service port for my thumb and found the relief valve but its not adjustable from the outside manual shows several washers but does not state if they are used for pressure relief . Thanks for good info Hornet825.
Ok I am unfamiliar with the way Komatsu has there main control valves set up. I work with alot of case, volvo and some deere equipment. But if you say there is shims in the circuit reliefe then you would have to disassemble the valve and komatsu should have a spec for the thickness of the shim to the pressure differencial it creates. But if you can't find that info, I would measure the thickness of the shims and try takeing out the thinessed one. And try to overcome the thumb cylinder with the bucket again. Then fine tune from there.
Jack345, did you figure out how to adjust the relief pressure for your thumb? I have the same machine (Komatsu pc78mr-6) and need to dial down the relief pressure for the thumb as bucket curl doesn't overcome thumb. Mine was factory plumbed and has a changeover valve (for breaker vs thumb as I understand it) and that has an adjustable relief but doesn't seem to affect thumb cylinder relief as I thought it would. Was the relief you found for yours on the main valve? Thanks!