When unscrewing nuts from studs, it is necessary to pre-clean the threaded part of the stud protruding above the nut with a metal brush in order to remove dirt and possible rust. This will prevent the nut from running through a contaminated thread. Before loosening the nut, treat the cleaned section of the thread with a rust remover. Many such solvents are available, so always follow the directions in the enclosed instructions for use.
In the case of unscrewing the bolts from the weld nuts of the body, it is desirable to treat these threaded connections with a rust remover from the inside of the body. The heads of such bolts, as well as the weld nuts themselves, break off quite often.
Threaded screws with heads for an ordinary or Phillips screwdriver can also be difficult to unscrew. Phillips screwdrivers often pop out of the slot, damaging it in the process. To exclude such phenomena, you can use screwdrivers for a regular or cross-shaped slot with a through metal rod passing through the screwdriver handle, installing the screw head in the slot and tapping with a hammer on its metal rod protruding above the screwdriver handle. In most cases, this method helps to loosen the threaded connection, and the screws are easily unscrewed.
Pic. 4. Protractor disc (up) for angular tightening of bolts and nuts. Bolts and screws with Torx heads (at the bottom)
In modern automotive industry, threaded fasteners with special heads are increasingly used, which somewhat resemble cross-heads in shape, but nevertheless differ from them. They are called Torx heads (see fig. 4). Tightening and dismantling of such fasteners is carried out using special nozzles that can be purchased in the tool kit. These attachments can also be used with wrenches with «ratchet», extension cords and other devices.
Hex socket or socket head bolts can also be difficult to loosen. As a first and necessary measure, the internal hexagon / polygon of the bolt head should be thoroughly cleaned of dirt and dust (e.g. with a small screwdriver) so that the plug-in hex or polyhedral key freely enters the entire depth into the bolt head. If possible, short inserts should be used that can be tapped with a hammer to overcome the inertial resistance of the thread before unscrewing. In some cases, however, a special Allen key is required. Sometimes, due to the small length of the wrench handle, it is difficult to loosen the bolts. We offer the following solution to such difficult situations: insert the key into the head of the bolt and put an extension on its handle, for example, some suitable socket wrench. Keeping the wrench fully seated in the head of the bolt, begin to turn it by the inserted extension. This prevents the hexagon socket from turning in the head of a firmly seated bolt due to slipping.
Pic. 11. Pipe wrench
Small and easily accessible hex head bolts can be loosened using a pipe wrench, one variant of which is shown in fig. 11, in cases where the edges of the hex wrench were brought up. Take care when handling the pipe wrench to avoid pinching your fingers.
Pic. 12. Using a nut splitter
Difficulties can also arise when loosening nuts and bolts with rounded edges due to the use of wrenches of the wrong size. Most often, this situation occurs on used cars. You can try to unscrew such nuts and bolts using a pipe (gas) key. Depending on the space available, such rolled nuts can be cut with a chisel or sawn with a hacksaw, running the blade along the thread. In this regard, we recommend using, if space permits, a special nut cracker (nut splitter). Its principle of operation is shown in Fig. 12: when the bolt is rotated, the nut is clamped until it snaps, then it is removed in two halves. The advantage of such a device is that it does not damage the thread of the bolt.
Attention! Do not leave your fingers in the place indicated by the arrow in fig. 11 because the key handles snap into place.
Self-locking nuts are often mentioned in the manual. From the very name of the nut, it follows that there is some kind of device that makes it difficult to unscrew the nut spontaneously and which is often destroyed when the connection is disassembled. Therefore, all self-locking nuts cannot be reused.
Pic. 13. Left-threaded extractor screws
Sometimes it happens that the head of the bolt breaks off. To extract the remaining threaded part of the bolt from the threaded hole, you need to drill a hole in the center of the bolt residue, into which a special extractor screw with a left-hand thread is screwed. Left-threaded extractor screws (pic. 13), which are screwed into prepared holes like bolts, are sold in specialized auto supply stores. In the process of tightening such a screw, its thread begins to cut into the body of the bolt fragment and drags it along, unscrewing it from the threaded hole. Another possibility for extracting a bolt fragment is drilling a hole with a diameter close to the diameter of the threaded hole in which the broken fragment of the bolt remains, and then screwing the thread-cutting tap into the drilled body of the fragment.
The studs are unscrewed and tightened with the help of two nuts locked one on top of the other on the threaded part.
Designed threads on aluminum parts often break when bolts are tightened. In such cases, special threaded inserts should be used. These inserts are screwed into damaged threaded holes according to the instructions contained on their packaging, or a part with a damaged threaded hole is delivered to the service station for new threading.
Tightening torques for threaded connections
The permissible tightening torque is indicated on the threaded fasteners of all critical assemblies and parts. To achieve the prescribed tightening torques, a torque wrench with interchangeable sockets/nozzles and sometimes an extension should be used. In many cases, it is not possible to get close to a particular bolt/nut to use a torque wrench, or the tightening torque is so small that it cannot be read from the torque wrench indicator. In such cases, the tightening torque is calculated by tightening (with a lot of experience) or controlled «by feeling» thread resistance. This applies primarily to threaded connections with a diameter of 6 and 7 mm.