Double Nut Method to Tighten Head Studs - XJ - Jag-lovers Forums

List: This may sound trivial but ,I used the double metholdof installing one of the head studs. I was wondering is there is a right way to use the double nuts.

Link to Hebei Bentley Technology

One: screw the first nut until it reaches the end of the threaded area and then screw the second nut until it stops against the first nut.

OR

Two: screw the first nut 2/3 of the way down the threaded area and then screw the second nut hand tight against the first. Then, using two wrenches, tighten the two nuts against one another: one wrench turning clockwise and the other, counterclockwise

I am using stainless steel nuts

The Devil is in the details.
emphasized text
Lou

Was Double Nut Method, Now Head Stud Installation.

OK, so I will use the Double Nut method with the nuts in the center of the threads.

So let’s move to the next step. As I related previously, I drained the coolant out of the block and blew the block thread out with compressed air. Despite that, when I lower a stick down into what I think is the threaded area of the block and withdraw it, there is about 1” of viscous yellow material on the stick. I assume this was too viscous to have drained out via gravity, or maybe it’s actually inside the threaded area that forms a small cup for the stud bottom.

I can think of one or two ways to deal with this. I could knock out the freeze plugs and wipe the threaded area clean, or stick something down the block holes (A giant Q-Tip) to absorb the moisture. I could also use a hack saw to make a vertical cut in the head stud threads so any moisture could squeeze out of the female threaded area (someone already suggested this). Or use compressed air at a low pressure move the moisture out of the female threads. .

Any opinions?

Thanks

If you want to learn more, please visit our website Double Head Screw Nut.

Lou

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It’s important not only to get moisture out, Lou - you have to ensure that there is no solid residue left either…

Mangling the studs with a hacksaw will not eliminate solid residue - and removing the freeze plugs, while efficacious, seems a bit overkill at this stage. Compressed air, and some bottom scraping should be enough…

However, the real proof of the pudding is that the relevant studs protrude equally when inserted - fairly easily checked. And it’s unlikely that none of the studs are seated…

As for double nutting; there is no point in tightening the studs beyond seating. As you torque up the head nuts, everything moves in the clockwise direction…

Frank
xj6 85 Sov Europe (UK/NZ)
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I do the second. The only reason is that if you make it tight against the end of the threading, and it slips just a bit as it often does as you are snugging the two together or tightening the stud in place, then when you remove the outer nut, the first one on can be bound against the end of the threading which then requires you to grasp the stud with pliers or something so you can get that nut off without loosening the stud again.

List:

I think the majority felt that putting the two nuts together in the middle of the thread was somewhat preferable to running them down to the bottom of the thread.

Done that way, one can grasp each nut with a wrench and tighten against one another and loosen, for removal, when done, without affecting the final location of the stud.

I think you could also use the same process for nuts driven to the end of the thread.

Lou

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I've never seen anything that I would consider official (pro or con) on the subject of using double nuts, but I've never been a fan for some reason. It just doesn't seem like a proper engineering approach to me; however, I wouldn't mind being able to make an educated decision. I'm not really sure the exact problem double nuts are intended to solve, though it seems to be suggested when people want a higher degree of confidence that a fastener is not going to back off. Does it really accomplish anything? If anybody can point me in the direction of where I can read up on this in order to speak more intelligently on the subject, I'd sure appreciate it. To quote NASA catalogue page 9.

Jam nuts. These nuts are normally "jammed" together
as shown in figure 7, although the "experts" cannot agree
on which nut should be on the bottom. However, this type
of assembly is too unpredictable to be reliable. If the innernut is torqued tighter than the outer nut, the inner nut will yield before the outer nut can pick up its full load. On the other hand hand, if the outer nut is tightened more than the inner nut, the inner nut unloads. Then the outer nut will yield before the inner nut can pick up its full load. It would be rare to fet the correcto amount of torque on each nut. A lock nut is a much more practical choice than a regular nut and a jam nut. However, a juam nut can be uses on a turnbuckle, where it does not carry any of the tension load.

Figure 7 shows the jam nut next to the mounting surface with the thicker nut on top.

Not certain if this applies fully to double nutting.
I know they use double nuts in many structural applications
where the loads are basically static. I see them all the time on monopole designs. That the use of double nuts is intended to prevent rotation of the fastener seems rather obvious. That should be a concern with any threaded fastener. Why jam nuts in particular would be chosen over the more widely used friction or chemical type locking devices is perhaps the better question. The intended application in this case is for use with pipe hangers in tanks containing diesel oil that will be inaccessible for the most part. I would have expected to see the use of nyloc nuts. If there had been a particular concern regarding loosening, then I probqably would have recommended Loctite. These joints are never going to come apart for any type of normal maintenance. I just never see jam nuts used so I'm trying to figure out why someone would choose this method over the others I mentioned. It seems a questionable solution at best. The first place I ever remember seeing 'Double nutting' was on pillar drills in my schools work shop.

They were used to set the 'plunge' height of the drill.

I used to have a list of approved fastening techniques for on UK military A/C, but can’t remember if jam nuts were on there.

I’ve certainly used them at home in situations where there is rotation or vibration(when I didn't have a nyloc or similar to hand), how well they work seems to depend on how well I manage to torque them against each other!

The thing I have used at work and seen used more is where you have a ‘screw’ that adjusts up and down in a threaded hole and then has a locking ring to set whatever displacement you come up with. I’ve used it on items subject to rotation with some success. I’ve seen it used on things like flow valves too. It’s the same basic principle but instead of 2 nuts you have a threaded hole and a nut.
I've seen them used in situations where there is an adjustment to be made. That's not the situation here.

If I was at home, if I was working on my car, or if I was in the middle of the ocean and needed to lock a fastener and had no other choice available, I'd use two nuts. In a heartbeat. I know will work to a certain extent. I'm trying to determine the engineering behind the use of jam nuts.

I'm not sure what help anecdotal evidence would be if I was trying to present an argument for or against. I was really looking for reasons why a jam nut would be chosen and the mechanism by which it works. If I know those two things, I'll understand when and why it should be used.

I do appreciate the response. It certainly doesn't seem like there's any consensus, but at least I know that generally, I'm not alone in my skepticism. You say your application is in a diesel tank.

For Nyloc, or for that matter thread lock, is there any compatibility issues between them and the diesel or other chemicals present?

My materials/chemistry is a bit rusty but I'd want to be sure that the diesel or any contaminants or solvents used when cleaning the tanks etc, wouldn't degrade the nyloc/threadlock.

If compatibility is an issue you could still look at all metal 'stiff nuts' or even something like wire locking or castellated nuts & split pin etc instead of jam nuts.

The link unclesyd gives explains how they work, essentially they 'pre-load' each other so they are less likely to become loose from vibration.

Thinking about it variations on the theme were used on aircraft stores as I recall. They were used on fuze pockets and the like I think. They were more like locking rings than actual nuts but used the same principle. However it was several years ago I was looking at such things and I can’t recall for sure.


thread311-

thread725-


Several of them reference the same link as unclesyd. I don't think compatibility is an issue. If the non-metallic insert could not withstand immersion in diesel oil, there are metallic versions available. While I haven't checked specifically for this application, Loctite has thread locking compounds for use in hydraulic systems. I don't think incompatibilty with petroleum products is an issue.

If I asked how to determine the proper torque on a bolt, would anybody think an example of how a bolt was torqued would be a good answer? Or that providing an example of a situation in which a bolt required torqueing would be of any help? None of that presents a compelling argument for their use. I understand they have worked or were used in this or that situation. That's not what I would consider engineering rationale for use anywhere else. Isn't the point of engineering to determine what's happening and why so that those lessons can be applied to other situations totally unrelated? That's always been my approach.

I have yet to see two references that are in agreement. There appears to be disagreement on the torqueing sequence and even the order of the nuts. I would like to see the "Handbook of Bolts and Bolted Joints" but I don't have access to it. I was hoping to find what I needed here, but I don't believe I'm getting anywhere.

I really appreciate all the well intentioned input. Thanks guys. My understanding is that in applications where the "structure" will undergo cyclic loading, double nutting especially with a jam nut and a structural nut are used when threaded fasteners other than high-strength bolts are used to insure the nut does not back off after installation. When using high-strength fasteners including ASTM A325 and A490 bolts, the bolts are installed by turning the nut beyond a snug tight condition producing a tension in the bolt material. This is the condition described in the AISC Manual of Steel Construction as a Type F fastener. This tension load in the fastener creates a friction effect at the nut which should hold it in place. However, for a variety of reasons, other threaded fasteners are often installed with two nuts, one of them being structural. The second nut is turned against the first to jam them together. This forces one nut against one side of its threads and the other nut against the opposite side. This locks the nuts together so they resist turning and keeps the nut from backing off under cyclic loads. I see this most often in mounting hardware for machinery but it is often used elsewhere. If you have the time, I commend the original cited article on using jam nuts. In that you will learn that the jam nut should placed against the material and the structural nut placed against the jam nut. I occasionally specify two structural nuts so I avoid the possibility of having the wrong nut placed against the material. Sorry for the long post.