i got a 290 Hitachi hoe I was testing today, and noticed a odd knocking occasionally. I think I narrowed it to the cylinder that moves the Arm in and out. If I extend the arm to maximum reach then set the boom down and press it down a bit so that the Arm is loaded in the extend position, if I then operate the arm cylinder in and out just very slightly it knocks, but if you watch the rod nothing is moving. Im convinced that the piston on the end of the cylinder rod has come loose and is able to move back and forth just slightly, causing the knock when it slams one way or the other. It seems unlikely that the piston come loose, but not impossible I imagine. What else could it be? The noise seems to dissipate as you go towards the engine area, but it really reverberates in the boom almost like someone is tapping on the boom with a small hammer when it does it. Any ideas?
It's actually entirely plausible that the piston is loose. Usually happens when the cylinder has been resealed by someone who doesn't have the wherewithal to tighten it properly. If you catch it before it leaves the chat altogether, you will have saved yourself a ton of heartache. On the other hand, it could be something else? Only you are there on the spot.
Yeah, I sure hope it will hang on for the classic “one more job”. As always no time to take it down. . As far as the cylinder, I don’t know if its ever been apart before. Not since Ive been around, but who knows. Has about 7K Hrs on the clock, and runs and operates fine…..for now anyway.
If the piston is loose, every time you hear the knocking it's also knocking off bits of metal to get carried around your hydraulic system. Know when to hold em, know when to fold em.......
This should be an easy fix. Probably no parts needed. Just some tools to tighten the piston if it is not significantly damaged already.
Many Hitachi/ Deere boom and arm cylinders use a cushion ring that slows the oil down as the ring enters the cylinder top head with the rod extended. The cushion ring floats and can move slightly back and forth. I have only heard the knocking sound on one machine a 350DLC arm cylinder but that’s all it was.
If it was up to me I would definitely pull it and have a look see. I wouldnt be willing to risk the potential of what could happen if it things go bad. As far as the cushion ring is that a metal piece ? This noise is very metallic almost uncomfortably loud if you put your ear right up against the boom. And it only seems to be doing it with the cylinder in the fully retracted position.
I didn’t have enough coffee yet apparently. Cushions are metallic pieces . There is also cushion in the end of the rod to slow down the oil as the cylinder approaches full retraction. I agree for everyone’s peace of mind take the cylinder apart for inspection , just don’t be surprised if you find no issues.
You're a gambler I see. If it's knocking that loud, it won't make another job. You could be replacing the entire cylinder if you don't correct the problem now. You mean like.... The piston coming completely off and bending the rod.? or....the rod breaking? or....the rod shattering and sending shrapnel in all directions? or....just fix it now.
I had my boom cylinders rebuilt last July at a reputable shop. But, a few months later this happened: I had CAT come check the machine...it felt like a major structural component had broken...they eventually tracked it down to the rebuilt cylinder. CAT found that the set screw was left out when they put it back together and the securing nut backed off. When it finally let go...well, the video shows that. You can read the whole thread at: HeavyEquipmentForums
No sir. I am not a gambler. Like I said, if it were up to me I would pull it. Its not up to me. Im just the lowly contractor who works on their equipment. I told them whats up and the consequences of letting it run that way. After that its not my decision.