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

[Welder Dave]

It can depend a lot on if there's vibration involved as to whether or not you need something extra to prevent a fastener coming loose. Other times it's just good practice to have a fail safe backup. The rep. for Nord-lock told me that even red Loctite can come loose due to vibration. There are some simple ways to keep fasteners from loosening. Castellated nuts with cotter pins, double nuts, metal tabs to bend against the nut, roll pins through the nut and shaft, safety wire, Nord-lock washers etc.

I'm sure there are cases where the original design had to be modified because of failure in the field. If locknuts were used it's best to replace them on critical applications or things that are a pain to have re-repair like hydraulic cylinders. It might not be a bad idea if aircraft standards were used on critical fasteners.

 

[terex herder]

I have rarely seen a properly designed threaded joint on the piston end of a cylinder rod. They are compromises between the stretched length from nut torque under the piston and the need for a compact cylinder.

A properly designed threaded joint will have a stretched length of at least 2 1/2 diameters. It's difficult to do when compactness is required.

 

[Welder Dave]

Factory cylinders have been known to loosen, pull the threads out if bolts are used and even break. Some are known to seize too and have to be cut off.

 

[HarleyHappy]

Of all the calamities that can happen on equipment, a piston nut or bolt backing off, is one my worst fears.
I have had it happen a few times over the years, so I am pretty anal about how I put them back.
I just did a Kubota cylinder last week and while I despise their compression rings, getting them on and then shrinking them, is the worst problem.
The nut spun off with my cordless impact. Had nothing for torque.
This time, I put the seal in hot water and stretched it on, I taped it with a couple of wraps of electrical tape. Usually I use a silicone hose clamp but this time, I used a SS zip tie with tool that I had bought a few years ago for hydraulic hose coverings.
Worked great, just slid off after everything cooled.
The nut, I used alcohol on the threads and nut and used Rockset to put it back on, dimpled three spots around the nut and put it back together. Before I put the nut on, I heated it up with a Mapp gas torch.
Probably took 2 hours total.