What can I do to keep the bolt from loosening? How to protect threaded connections from unscrewing. A bolt stuck: how to unscrew

Car repair is a constant job of loosening and tightening bolts, nuts, screws, studs, etc. Sometimes to unscrew one nut or bolt it takes a lot of time, especially if it is located inconveniently, and even rusted.

It is very difficult when repairs are carried out by a novice motorist.

Basically, we make problems for ourselves, because we are too lazy to take a suitable tool that lies on the next shelf, we are always in a hurry somewhere and, as a result, tear off the edges on nuts and bolts.

How to unscrew a rusty bolt or nut

If you can see that the nut has rusted and didn’t go the first time, it’s better to stop. First, clean the protruding end of the thread with a metal brush, then apply WD 40 type grease to the thread and nut, after a short wait, try to unscrew it only with a non-open-end wrench, take a better head or ring wrench, if you don’t have one, ask a neighbor, do not be shy, otherwise you will break the edges, then there will be more suffering.
If that doesn't help, then apply WD 40 again and wait a little longer, tap with a hammer through some kind of spacer.

How to unscrew a broken bolt or nut

When loosening nuts and bolts with damaged edges, it is also better to use a box wrench or socket.
If it does not fit, you can tap a little with a hammer and turn it off, then change it to a new one.

In the case when there are almost no faces, we look for a small adjustable wrench and try. It should work.
Does not work?! Then we make a groove with a sharp chisel and strike at an angle in the direction of unscrewing, the nuts usually turn away, if not, then the nut can be cut in half, and the bolt will have to be cut and drilled.

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Sometimes even small screws with slots and cross slots can stick very strongly, in this case, take a good screwdriver and hit the handle with a hammer to turn it out.
You can also use an impact screwdriver, hitting the edge of the cap in the direction of unscrewing.

Hairpins. They do not have edges for which the key can catch.
Screw two nuts onto the free part of the thread and lock them by tightening them towards each other. Unscrew the stud by the lower nut.

How to unscrew a broken bolt or screw

A broken bolt or screw has to be drilled out, how to do it correctly so as not to damage the thread?

First, file down the fracture site with a file or at least a large needle file to facilitate punching.
Try to pin right in the center and well.
Drill out the bolt, the drill diameter should be approximately 0.8 of the thread diameter, for example M8 thread - 6.4 mm drill. A More Accurate Table of Thread Hole Diameters Large bolts are first drilled with a small drill bit.

Remove the rest of the bolt and go through the thread with a tap.

It often happens when the thread is torn off, it’s good if it’s on a bolt, it’s easier to change it to another, worse when in detail. If several turns are torn off or the thread is crumpled, try to go through with a tap.
If the wall thickness allows, we cut a new one.
To do this, we drill a hole for the next diameter, for example, M6 was torn off, the next M7 or M8 (M8 is more common), we drill carefully with oil.

Now we cut a new thread.

First, with a tap with 1 number, slowly periodically turning it out half a turn, to clean it from chips, if the hole is deep and deaf, then turn it out to the end. After cutting, blow the hole and the tap, cut it with the second number, as well as the first.
There are also universal taps that replace number 1 and 2.
Do it carefully, lubricate it often and turn it back out so as not to break it.

When assembling parts, wash all bolts and nuts in gasoline or acetone. Lubricate the thread with oil or grease.
In nodes that work with high temperatures It is better to lubricate the thread with graphite grease, but in no case not with oil or grease, otherwise you will not turn it off later, the oil and grease will simply coke.

P.S.: Which way to unscrew the bolt. It's strange but many people don't know.
Ordinary bolts and nuts are unscrewed counterclockwise, and twisted clockwise.

Among detachable connections threaded takes first place both in prevalence and reliability. However, in practice there are many cases when unscrewing a threaded pair is not easy.

The reasons why it is not possible to unscrew the stuck nut (bolt).

There are several reasons why it may be difficult or even impossible to disassemble this simplest connection:

• deformation of the thread or connection details, for example, with a strong impact;
• twisting not along the thread with the application of significant force - in this case, friction between the surfaces of the parts increases significantly (the effect may be aggravated due to the influence of external factors);
• oxidation of the surfaces of the connection parts, the formation of a layer of rust on them;
• diffusion of materials between the details of the connection.

The last two reasons are well known to almost everyone, especially motorists.

The problem is that studs, bolts and nuts are most often made of carbon steel. With prolonged contact with water and oxygen in the air (for example, bolts on a wheel are constantly exposed to such an effect), these substances penetrate into the smallest gaps, including between the parts of a threaded connection. As a result, iron oxidizes, forming a layer of rust, which increases friction. It will take a huge effort to move the parts from their place (often the value exceeds the strength of the bolt, and it collapses).

Designers try to avoid such troubles by using parts with protective coatings or made of stainless steels for connections. But that doesn't always work either. If the bolt and nut are exposed to heat (muffler parts are an example) protective coatings can be broken, corrosion processes are accelerated.

There is also a process of diffusion (mutual penetration) of materials, the parts form a monolith, which becomes difficult to disassemble (this phenomenon is often encountered by those who try to unscrew the bolt on the crankshaft).

How to unscrew a stuck bolt (nut) - the main methods.

To cope with this task, several methods are used. They can be roughly divided into

• mechanical;
• physical;
• chemical.

mechanical methods.

These include methods that allow you to disassemble a threaded connection due to the application of mechanical forces:

• the use of ring wrenches and sockets instead of open-end wrenches;
• using leverage to increase effort;
• impact with a variable direction of force;
• accentuated impact (short-term application of significant effort or effort at certain points);
• shock destruction of layers of oxides and rust.

An open-end wrench covers only three faces of a nut or bolt head. In addition, there is some gap between it and the edges. In this case, applying enough force to unscrew it can be a problem - the key can break off and “lick off” the edges. Ring wrench or end head cover all edges, which allows you to apply more force.

To increase the effort, you can use the lever - increase the length of the handle. At the same time, there is a danger of licking the edges or destroying the fasteners. You can also damage those parts that were connected by a threaded pair.

Often, a change in direction helps to unscrew a stuck or rusted nut - before unscrewing the connection, they try to screw it up. The impact of forces alternately in different directions destroys layers of rust, giving way to the details of the connection.

An example of the application of short-term significant force is given by the method using a chisel and a hammer. A notch is made on the edge, a chisel is pressed into it (directing it in the direction of unscrewing the nut) and hit with a hammer. In this case, the impact force is much greater than that which can be applied using wrench. Since the impact is short-term, it cannot destroy the bolt.

Note! In this way, you can also unscrew the nut with torn edges. This is somewhat easier than trying to file new ones for a smaller key size.

Light tapping of the nut and/or bolt with a hammer will shake the entire structure and destroy the rust layer. It is only necessary to dose the impact force so as not to damage the parts, not to deform the thread. Although, as one of the methods for disassembling a “recalcitrant” connection, destruction of the nut with such blows is suitable. The only problem is that the threaded pair will have to be changed.

Physical methods.

Some of them are based on physical properties metals. Of these, only one is widely used - heating the parts of the connection. In this case, the material of the nut expands, the gap between it and the bolt increases, and it becomes easier to unscrew it. If you heat up the entire structure, you can destroy the resulting rust, which will also give positive result. Use for this purpose should be any source of heat - a powerful soldering iron, building hair dryer, blowtorch or other sources of open fire.

Important! It is dangerous to use an open flame near wood, combustible plastic or flammable liquids!

good replacement open fire will become electric heating. For this, a transformer (factory or home-made) with a secondary winding with a voltage of 1.1 - 1.5 V and a maximum current strength is suitable. Through copper cables and clamps secondary winding closes on a bolt that must be unscrewed. Heating occurs, after which the transformer is turned off, the connection is dismantled.

Other physical methods use the method of wetting surfaces to reduce friction. For example, if you allow liquid to enter the space between the bolt and nut through the smallest channels, the friction between the threads will decrease and it will become easier to disassemble the pair.

From easily penetrating liquids, you can use those that are always at hand with the motorist:

• brake fluid;
• antifreeze;
• kerosene;
• gasoline;
• diesel fuel.

The first two contain glycols and ethers - substances with great penetrating power. The rest are aliphatic hydrocarbons and have a similar effect.

The second group also includes such solvents as whitesprit and turpentine. All of them can be used to unscrew the stuck nut. The processes are somewhat different only in time.

The method is simple - wet a rag and put it on the stuck parts. Penetrating into gaps and pores, liquids lubricate surfaces and loosen rust layers. After some time (from half an hour to 3-4 hours), you can try to unwind the connection. If disassembly fails, repeat the process. You can speed it up with periodic light tapping.

The same fluids are the basis for "liquid keys" - lubricants special composition that are offered in car dealerships.

One of the most popular among motorists is WD-40, which includes mineral oil, white spirit and volatile gasoline. The effectiveness of such a "cocktail" has been tested in practice, it copes with rusted nuts in half an hour.

Note! If the nut is stuck not due to water ingress, but under the influence of temperatures, the effectiveness of WD-40 is significantly reduced.

Chemical methods.

Their action is based on the chemical destruction of rust formed between the parts of the connection. This requires that active chemicals get into the gaps between the bolt and nut.

Almost any acids are used for such processing of threaded joints:

• sulfuric;
• salt;
• acetic;
• lemon;
• orthophosphoric, etc.

Sulfuric acid for battery electrolyte or hydrochloric acid for soldering radiators use this way:

• a rim is organized around the nut or head of the plasticine bolt;
• inside the resulting "capacity" make a few drops of acid;
• a piece of zinc activates the process, creating a galvanic couple.

A day after the start of such processing, any connection is untwisted.

Weaker acids are less effective, either a significant amount or more time is required.

Note! Orthophosphoric acid is found in beverages such as Coca-Cola. That is why you can try to unscrew the nut with their help. But its concentration is low, the acid itself has low activity, so such treatment is effective only in "mild" cases.

If nothing helps.

If you still failed to unscrew the nut, the connection can be destroyed - cut off with a grinder.

Another method is to drill out the bolt with a drill.

But before resorting to such methods, you should evaluate all the consequences!

Video.

Boris DAKHNOVSKY

Lever torque wrench. Simple, cheap, reliable and fairly accurate.

Well, the repair is entering the final stage - it's time to start assembling. How are nuts and bolts usually tightened? "From the heart"! One will pull up, and then another foot will rest against something - to "tightly". Another will put a pipe on the key, and insert a crowbar into it ...

In fact, all fasteners are designed to be tightened with a strictly defined force - in technology it is called a moment. Not less than necessary (or it really will unscrew), but not large (you will tear off the thread) ... But where is it - this golden mean? A torque wrench will tell you - it will measure and show you the magnitude of the moment-force. And those keys that are the most modern will also “prompt” aloud when enough is enough.

The oldest torque wrenches are equipped with a round scale and a mechanism similar to a watch. In them, when a bolt or nut is tightened, a thick steel rod is twisted, and very slightly. The gear reducer multiplies this tiny movement many times over, and the pointer on the scale rotates just enough for the mechanic to gauge the force being applied to the fastener. This device does not differ in particular accuracy, especially not new: as the mechanism wears out, the gaps in the gears and their axes cause backlash of the arrow, and sometimes jamming.

Later they came up with a simpler tool. A rod of a strictly defined rigidity and length is attached to the base of the square key (for a hexagonal head). And at the other end is a pen with a scale.

An arrow is attached to the square. When the mechanic tightens the nut, the rod bends, and the arrow, always fixed relative to the square, shows the force on the scale that has shifted along with the end of the rod. This is a very simple and cheap tool. And if the manufacturer exactly withstood the manufacturing technology, then the most reliable one. From old age, the rod can be deformed - the arrow in the free state will not point to zero. To restore accuracy to the device, bend the arrow - it is made of mild steel.

The most modern, sophisticated torque wrenches are more likely to be used in specialized workshops or on a factory assembly line. They have a scale that vaguely resembles a micrometer scale, and, guided by it, you can very accurately set the required force. When it is reached, there will be a loud click, and the hand will feel a return. So, with this nut finished - it's time to move on to the next one. Such a tool is very convenient if, for example, you need to pull off the crankcase halves - tighten 20-25 bolts with the same force. With less monotonous work, it is tedious to rebuild the device for “your” force for each nut - it is more convenient to use a simpler tool here.

Micrometer scale

With what force to tighten the fasteners - this can be found in the repair instructions. Do not rely on your own experience and do not try to use "someone else's" documentation. Even on motorcycles of similar design, fasteners for identical assemblies should be tightened with different forces (see Table 2). It may differ several times! If suddenly you do not find recommendations, then the nut or bolt is standard, and they must be tightened with a standardized force (see Table 1).

For complex parts tightened with many bolts, the instructions provide a diagram showing the tightening sequence. If it is not observed, it is possible to warp the entire assembly, a leak will form or some shaft will jam. There are several bolts, and the sequence of their fastening is not indicated? So, they need to be tightened crosswise. And gradually, in several steps, until the torque wrench shows the right moment.

Modern torque wrench

When reading the tightening torque table, pay attention to the notes. They may stipulate special conditions assemblies. For example, that the threads should be lubricated with oil or thread sealant before tightening ... If additional requirements no, it is understood that the fasteners must be clean and dry. And preferably neither strongly chilled nor hot - at room temperature.

Material source: MOTO magazine

There is probably no such person in the world who has not tightened or unscrewed bolts at least once in his life. These fasteners are in abundance everywhere, they have been known since time immemorial and are used far from only in the automotive industry. However, as it turns out, white spots in the operation of such a seemingly well-known part are still present. One of them is the following riddle: “Does it really take less effort to loosen a bolt than it does to tighten it?*” You will find the answer to this question below.

* Naturally, we are not talking about stuck or rusted fasteners.

The experiment shown in the video does not claim to be scientifically accurate, but it seemed to us quite plausible, although its results are not very logical. After reading the materials on resources devoted to the subject of various hardware and other threaded connections, the rule for applying force is as follows: “when unscrewing, a moment of 1.3-1.5 times more is required than when tightening.” The thing is that when one thread enters another, a load is formed, due to which the mutual penetration of materials in this zone occurs. Therefore, technically, if you like, scientific point vision, when unscrewing it will take more effort. More:

But let's move on to a quick review of the video.

From the video description:

As Charlie Chaplin discovered during his short career as an assemblyman, depicted in the 1936 film Modern Times, hand-tightening bolts all day long can be a real headache. Luckily for Charlie, and for any of us who have ever taken a wrench to loosen another bolt or nut, loosening means less physical energy, it just takes less torque originally invested in tightening the bolt.

Why is this happening? Magic? After all, what reasoning comes to mind in this case? So I took a bolt or nut and tightened them with a torque of 100 Nm. If I immediately unscrew the connected element, I need exactly the same amount of effort - the peak torque will be 100 Newton meters. The only difference will be in the applied direction of effort.

As explained in the following video, this is not the case. The YouTube channel "AvE" explains in detail and clearly shows why this seeming axiom never works.

abstract

The theorem is based on the following conclusion: it will always be easier to loosen a threaded connection, since the thread itself acts inherently as an inclined plane.

Tightening a fastener is compared to going uphill, and loosening it corresponds to going downhill. In a test conducted by a tech blogger, it took 4 percent less torque to loosen a bolt than it took to tighten it.

The experimenter especially emphasizes that the test was carried out in a short period of time and the thread could not physically “shrink”, rust, and so on, that is, come into its working condition during long-term operation. This is a very important point.

I can hardly tell all the details based on this video, translating from technical English into Russian is not the best simple task, but in in general terms The following is happening in the video:

To measure the torque, a certain sensor was created, with the help of which the torque force measured in kilopascals is translated into an electrical discharge measured in millivolts.

When tightening / loosening the bolt with a hydraulic wrench, the sensor readings are transmitted to an oscilloscope, which reflects an increase or decrease in torque on a running graph.

The experiment after 5 minutes of chatter starts with 6 minutes of video.

Techies will understand what is happening on the video, the rest will have to take their word for it.

The data turned out as follows: the tightening force converted to millivolts was 800, but when unscrewing the maximum starting torque was lower - 776 millivolts. That is 4% less.

The experiment involved a new, clean thread without lubrication.

It doesn't matter if you have a bike, a car, furniture, or anything else. But you definitely had such a situation when the nut was unscrewed on its own. What needs to be done so that the nut does not unscrew? You will learn more about this in the video tutorial.

You can use a traditional nut and bolt, but it won't save you from getting loose. Using a torque wrench, tighten the nut by hand, but with high vibrations, it will begin to unscrew. To hold, we need to tighten another lock nut from above. With the help of a lock nut, we can stop the unwinding of a regular nut, but this does not give a 100% guarantee. It is a disposable product.

You can use a traditional grower washer, it is disposable and can be unscrewed from vibration. It is possible to replace a regular nut with a flanged nut with a wide bearing surface and special notches. They dig into the support pad, but a nut with a flange does not give us a 100% guarantee.

toothed washers

One of the more popular and inexpensive solutions would be a toothed washer. It has a reliable contact with the entire surface and a low price. The main problem that arises is that you can overtighten and thereby flatten the teeth. Thus, they turn into an ordinary flat washer.

Serrated washers can only be used up to the specified torque. Highly important point when using, do not overtighten the nut and thereby smooth the washer. The low price of toothed washers will help solve the local loosening of the nut. Only two options will give us a 100% guarantee.

wedge washer

The wedge washer is a system consisting of two washers. These washers are used in pairs and tightened to the required torque. The trick is that the angle of the inner wedges is higher than the angle of the thread. In this connection, spontaneous unscrewing becomes impossible.

In order to unscrew the nut, we need to make more efforts than when tightening. The wedge washer gives a 100% guarantee against spontaneous unscrewing.

Anaerobic thread lockers

Another reliable and convenient way fixing the nut, is the use of an anaerobic thread lock. To do this, we need to apply liquid to the place of the thread where the nut will be. It is quite flowy and spreads easily over the bolt.

We screw the nut onto the bolt and wait, nothing else needs to be done. After some time, the latch will harden and the structure will not be collapsible. In order to unscrew, we need to heat up or make more efforts while working with a key.

We hope this video tutorial was useful and interesting. Write your comments, ask questions with pleasure we will answer. Recommend to your friends and acquaintances.