Cylinder rebuilt in shop in 2023 had rod nut back off during use.

I am not going to name or shame the shop because I am hopeful they will work this out. It should not happen. Mfg torque spec 2000 ft lbs + Loctite. No evidence of loctite. I highly doubt torque spec was met. Komatsu WB140-2 arm cylinder. Nut clearly backed off until two threads were remaining then sheared the threads. The shop in 2023 manufactured a new rod. The new rod has the stripped threads. The original is in the foreground. They are the same size just looks different from perspective. Advice?

I’m surprised it don’t happen more often. Especially, with the techniques & methods I regularly see deployed by our very own, on the HEF.

Check your hydraulic filters. There's likely some debris from those threads in your system. We've had 3 cylinders do that on 3 different Bedrock brand rippers. We always found metal in the filters afterward. I respect your willingness to work with the shop and your restraint in not naming them. If they are any good they'll want to know about it and take care of you. Even the best shops make mistakes.

The National 1100 series boom truck I operated had the nut back off on what was presumed to be a factory assembled boom extension cylinder, while I had a load on it.

I had the bolt on my Cat stick cylinder pull out and damage the threads in the rod. I'm pretty certain the bolt had been loose for quite awhile. I was driving over a hill and the bucket contacted the ground. Not real hard but I heard a bang and had no stick movement. Shop was going to make a new rod but I suggested just threading the rod for the next size up bolt. They said that would work and be about $300 less expensive. I'm not sure if they could build up your rod with weld or spray welding and retread it. They should give you warranty or at least a pretty big discount.

That sucks that it happened, but 3 years after the work was done? Maybe if they are a really good shop they give you a discount but I wouldn't hold my breath waiting.

That does suck and hopefully there is minimal damage or issues so you can reuse most parts. I don't have any recommendations but I am a bit surprised that cylinder nuts are not pinned, castellated, or such to keep them from moving. Even a simple retaining washer with the tabs you bend up would be beneficial.

LCA078 said: I am a bit surprised that cylinder nuts are not pinned, castellated, or such to keep them from moving. Click to expand... Usually the combination of a Nyloc nut and Loctite plus the appropriate torque - often somewhere in the range of 5000 ft lbs for a large cylinder. I’ve never seen one tightened that way come loose.

Yes, a Nyloc nut with loctite and cranked down ‘should’ be sufficient. But a simple retaining washer is physically better. Maybe the engineers don’t want to compromise the strength of the threaded area with slots or pins which I understand…but don’t necessarily agree. I guess I’m just used to critical nuts and bolts in aviation being safety wired, pinned, or secured some way from backing out. Although the cylinder rod nut isn’t quite a Jesus nut, it’s pretty close.

I don’t see any damage in the cylinder, I hope. I have a distinct way of tightening piston nuts and while I have never had one of mine fail, it could definitely happen. Think the shop should take care of you. It looks like the rod could be re-used, even with those missing threads but would like to see Red Locktite this time. lol Good luck!

I never had one come loose back in the day. Now days I'd be using the Orange loctite on them. No not red. Never use red unless you like to use lots of heat and or never remove the part. Loctite is most never used properly, the threads can have no oil film at all and best to use the loctite primer. For aluminum, that is a non reactive metal, primer is a must, for any anaerobic loctite product.

Well, you have two rods available. Take the one with a better sealing surface and skip the loctite 'glue'. Crank on your nut and use some good metal glue. I promise it won't back out....

I recently bought some Rockset for some ear protection devices and have been giving that a thought over Locktite. I know when I start to heat a nut to pull off, if Locktite was used and by the smell, I can usually tell what color. I have always used red for cylinders because the alternative, could really make for a bad day. I will even stipple the threads if possible. I have always kept my eye out for a torque multiplier but am not interested in the HF stuff, with the tension rod as I think that would be in the way half the time I need it.

HarleyHappy said: I will even stipple the threads if possible. Click to expand... That's interesting because I grew up with a father who was a tool and die maker for the military. Calling him a machinist, or even a master machinist, was insulting to him, but he did teach me how to ensure a screw never backed out of anything by disrupting few threads up near the head. Same thing with set screws- a few precise dings on the threads with a sharpened punch was enough to ensure it wouldn't move on its own. He taught me that by disrupting the threads you could 'feel' the resistance change when you screwed it and thus you knew exactly how much force it would take to back it out. If it wasn't enough resistance, you simply added another ding or two. If it was too much and the screw would get stuck, then you just used another screw. Point is you knew exactly how much force it would take to remove that screw unlike loctite or such where you hope it's 'just right'. Loctite was a dirty word to him....

If there's room Nord-Lock washers would be a good option. They also have Nord-Lock extreme for even better bolt retention.

Coaldust said: I’m surprised it don’t happen more often. Especially, with the techniques & methods I regularly see deployed by our very own, on the HEF. Click to expand... What do you mean that running a nut on with 3/4 battery impact isn’t enough when it’s normally torqued to 8000 ft lb by spec???

Best Locktite ever designed, whack a few threads with a hammer.

Another idea is to drill/tap a decent sized set screw through one of the rod nut flats. Doesn't even have to a set screw as it could be a cap screw or small bolt to be a locking screw. Crank on your big nut, then crank down on your locking screw. Or even a modification of Harley's idea: Drill a hole through the flat of your rod nut and crank it down on your rod. Use a punch and disrupt the visible threads in the hole. Lots of ways to make this work in the field....

At a coal mine where I ran the shop we had three D550B articulated haul trucks that used three stage shot gun cylinders to lift the boxes. The pistons were captured with a large nut and the nut was drilled and two set screws were screwed in, one to upset the threads on the rod and another on top to prevent the bottom one from coming loose. All three trucks had the pistons come loose and send trash into the hydraulic systems. The box lift and steering systems were separated by a shuttle valve, one of Cat's supposed ball resolvers. The trash went from the cylinders, hit that shuttle valve and joined the steering system directly to the return to the reservoir. First truck it happened to was driving a high bank in third gear and suddenly turned to the right and dove off the bank and nearly ended itself and possibly the driver down a very high wall. Later on while I was employed by the Cat dealer in my area, Cat decided to employ that idea again for excavators and some dozers putting a linear encoder inside the cylinders. The same thing happened again and the cylinder shop was swamped with warranty claims. I'm not a fan of spiking threads to hold a piston rod nut on. I've had a mechanical engineer tell me on the truck catastrophe that a properly designed threaded retainer will not come loose when the proper amount of torque is applied at assembly. Doing the Sherlock thinking, if a nut or bolt comes loose in operation it wasn't assembled properly or the design was faulty. Going further then, the use of extra procedures to ensure a nut or bolt doesn't come loose is either meant as a feel good procedure for a bad design or the idea that someone in the field does not have the capability to follow the correct procedure of assembly. I've used lots of red and blue Locktite for years knowing it most likely was making me feel better about my reassembly. I haven't spiked a thread since I was apprentice almost fifty years ago.

John C. said: ……a properly designed threaded retainer will not come loose when the proper amount of torque is applied at assembly. Doing the Sherlock thinking, if a nut or bolt comes loose in operation it wasn't assembled properly or the design was faulty. Click to expand... 100% agree, and in the case under discussion it is unlikely that the design was faulty. QED.