Loosening a rusted fastener
Before loosening a rusted nut or bolt, remove dirt and rust from the adjacent bolt threads. Otherwise, it is the friction at the ends of the thread that is too great, and therefore the bolt breaks.
Clean the free part of the thread with a wire brush and treat with a rust remover. If you are using a quick acting rust remover, you can start loosening the nuts right away. If you are using a conventional neutralizer, you should wait a while before you start unscrewing the rusted fasteners.
• Use a wire brush to clean the threads, then use an aerosol can to apply a rust remover to the surface of the threads.
• If the rust remover acts quickly, loosen the nut immediately.
Other rust removers (oil, kerosene, diesel fuel, etc.) should work on rust for some time.
PRACTICAL ADVICE
Self-locking nuts
Self-locking nuts sit firmly on the threads and will not loosen when vibrated. To do this, they have plastic inserts or a slightly offset thread. Self-locking nuts are used only once, with repeated use their locking effect deteriorates.
Loosening damaged nuts
If you have torn off the edges of the hex nut with an open-end wrench or rust has severely damaged the surface of the nut, then only force will help to unscrew them.
Unscrew the nut, firmly grasping it with an adjustable (gas) key.
• If this does not help, the nut is cut off with a sharp chisel. In such cases, workshops often use a special device, the so-called «wrench».
• In well-accessible places, the nut can be sawn along the thread with a hacksaw.
Loosening bolts with an internal hexagon head or an internal «star-shaped» head
Before starting to loosen the bolt, remove any dirt from the bolt head.
These bolts are best used with long hex or «stellate» heads.
Unlike conventional wrenches (they always apply force diagonally) the heads inserted into the adapter also withstand a hammer blow. A blow - if necessary, directly on the head of the bolt - often loosens the bolt seat and makes it easier to loosen.
Loosening slotted and cross head screws
Even after a relatively short operating time, the screws can rust so badly that a normal screwdriver will no longer help here. With Phillips screws, the situation is even more complicated: with strong pressure on the screwdriver handle, the end of the screwdriver pops out. As a consequence of this, after several attempts, the cross-shaped slot is cut off and the screw can hardly be unscrewed.
• If the screw does not come off immediately, take a screwdriver with a firm handle and hit the handle with a hard hammer to try to unscrew the screw connection.
Often this is enough, since most often the rust layer at the head of the screw is broken by a hammer blow, and after that the screw easily turns out.
• If this does not help, use an impact screwdriver. After each blow with a hammer on the back side of the handle of an impact screwdriver, its working part is rotated. This tool allows you to remove almost any screw.
Removing a fixing connection by drilling
If the bolt head cannot be removed with a tool, only drilling will help.
• First, drill out the head of the bolt with a large diameter drill bit. If necessary, a preparatory hole can be drilled in the center of the bolt head beforehand with a small drill.
• Without a head, the bolt is knocked out either with a punch, or it is turned out from the reverse side with the help of pliers.
If this fails, carefully drill through the threaded part with a drill bit smaller than the diameter of the corresponding thread, and remove the remaining metal.
PRACTICAL ADVICE
Work in hard-to-reach places
If you need to drive a screw in a hard-to-reach place, you can pre-fasten it to the tool with body putty, chewing gum, viscous lubricant or a strip of tape.
Loosening the studs
Since the studs cannot be unscrewed with a normal tool, do the following.
On the free threaded part of the stud, very tightly screw two nuts one after the other (hide). When unscrewing, the wrench captures the lower nut, when screwing in, the upper nut.
Drilling bolts with sheared heads
It is important to damage the thread as little as possible.
• With a center punch, mark the place for the drill in the center of the remains of the bolt.
• Drill out the rest of the bolt: for bolt sizes up to M8, you can use a drill for a threaded hole. The threaded hole is the diameter of the bolt without threading. For bolt sizes up to M6, the rule applies: the thread diameter is multiplied by 0.8. Example: threaded connection M6 x 0.8 = threaded hole diameter - 4.8. Bolts with a thread size larger than M8 should be pre-drilled with a thinner drill bit.
Remaining metal residues in the threads are removed using a scriber or a magnetic rod. However, in most cases it will be necessary to re-thread the thread.
Thread cutting
Since light metal has less strength than steel, the threads in it are very easily damaged. If there is enough metal around the old thread, you can cut a larger diameter thread. Otherwise, have a workshop insert a threaded bushing in this place. Recutting an old thread or cutting a new thread is done in three steps. Therefore, the corresponding taps are called draft tap, 1st number (one neck ring), intermediate tap, 2nd number (two neck rings) and finishing tap, 3rd number (without rings or three rings on the neck).
• The pre-drilled hole is permanently lubricated with oil. Starting from the draft, the taps are sequentially screwed in and out.
In order not to disrupt the tap, cutting is carried out by slight turns forward (maximum 1/8 turn). Then the tap turns back until the metal chips break off, this prevents the tap from clamping in the hole.
TECHNICAL DICTIONARY
Bolt sizes and tightening torques
For normal bolts and nuts, standard tightening torques are sufficient. Wrapping simple fasteners, experienced mechanics feel the tightening torque by hand. If they do not trust this feeling, they use a torque wrench. For the most common bolted connections, the following tightening torques apply:
| Thread diameter, mm | 6 | 8 | 10 | 12 | 14 |
| Tightening torque, Nm* | 10 | 25 | 49 | 85 | 135 |
* The tightening torques shown do not apply to special fasteners and connections in light metals.
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