Restoration of threaded connections

Almost all car repair operations involve loosening nuts, bolts and screws. Over time, threaded connections rust, turn sour, the edges of bolts and nuts are damaged, screw slots break off and loosening becomes a problem. Below are tips to help you get the job done.

Loosening rusty threaded connections

Before installing a wrench on a heavily rusted nut, clean the protruding part of the thread from dirt and corrosion.

1. Clean the threads with a wire brush and apply a penetrating agent to the threads.

2. When using a quick-release compound, start loosening the nut immediately after applying it.

3. When using a slow release compound, begin disassembling the assembly after the penetration time has elapsed.

Loosening damaged nuts

If the nut edges are damaged, use special tools:

• tighten the nut with an adjustable collet wrench. Perhaps this will be enough to turn her away;
• cut the nut with a sharpened chisel;
• if the nut is well accessible, then it can be sawn along the axis; with this method, the bolt thread is not damaged;
• carefully, without damaging the threads, use a special tool for cracking nuts.

Note. In threaded connections, self-locking nuts with a Teflon insert are very often used. After unscrewing such a nut, replace it with a new one, since the functions of locking the old nut are lost after unscrewing.

Bolts with hexagon socket head or polygonal head

To remove such bolts, clean their inner hole in the head and use the appropriate wrench. A set of hex wrenches or multi-toothed wrenches is best suited for this purpose. Before removing the bolt, tap the head with a hammer carefully so as not to damage the head - this can make it easier to remove the bolt.

Removing self-tapping screws with slots and Phillips

Sometimes heavily rusted connections cannot be unscrewed with a screwdriver. After several unsuccessful attempts, the slot is crushed and it becomes impossible to unscrew the screw in the usual way.

1. If the screw cannot be removed, take a suitable screwdriver and try to remove it by hitting the screwdriver handle with a hammer.

2. If the screw is broken, drill out the rest of the screw.



3. If you cannot remove the screw by hand, use an impact screwdriver.

Screwing in and out of studs

The stud has no surface for the key to catch on, so follow the steps below to remove the stud.

1. Screw two nuts onto the free threaded part and lock them, turning towards each other.

2. Having fixed the nuts in this way, unscrew the stud.

Drilling out a broken bolt

The threaded hole in which part of the bolt remains can be left undamaged by doing the following.

1. Point the bolt fragment exactly in the center. To facilitate punching, file the break with a file, if possible.

2. Drill out the broken bolt. The drill diameter should be 0.8 of the thread diameter. For example, for an M6 threaded connection, the drill diameter should be 4.8 mm.


3. To drill large bolts, use a small diameter drill first.

4. Remove the parts of the bolt left after drilling and «pass» tap thread.

Thread cutting

Very often, during the repair process, it becomes necessary to restore a damaged thread or cut a new one.

In light-alloy metals, the thread is cut quite easily, since, unlike steel, their hardness is low. If it is not possible to cut a suitable size thread, cut a larger size thread.

Restoring a crumpled, damaged thread or cutting a new one takes place in three stages, the thread is cut successively with three taps: first, with a tap with the first number (it has one annular groove on the shank), then tap with the second number (with two annular grooves on the shank) and finally the tap with the third number (with three annular grooves or without grooves). Before screwing, the taps must be lubricated with oil.

In order to prevent the tap from breaking when threading, turn it back periodically to clean it from the resulting chips.