Useful tips for repairmen (Audi A4 B6)

A threaded connection that cannot be unscrewed or a stripped bolt often force amateur fitters to abandon the idea of self-repair. The following tips are intended to help beginners when performing unfamiliar work operations.

Loosening rusted screw connections

Before applying a wrench to a rusted nut or bolt, clean any dirt or rust from the exposed threads, otherwise the bolt will be twisted when unscrewed.

• Clean the threads with a wire brush, then spray them with rust remover.
• In case of a fast-acting agent, unscrew the nut immediately. Otherwise, wait a while before unscrewing the nut.

Loosening damaged nuts

If the edges of the nut have already become rounded from previous attempts to unscrew it, or if rust has deformed the surface to which the wrench is applied, then in this case the nut can only be unscrewed by applying force.

• The first option is to use gripping pliers. The pliers allow you to firmly grip the nut and then unscrew it.
• If pliers don't help, try chiselling the nut out with a chisel.
• If the nut is easy to get to, it can be sawed along the thread with a metal saw. In workshops, a special device for breaking nuts is used to remove such nuts.

Handling self-locking nuts

Self-locking nuts are tightly fastened on the thread, they do not loosen even under vibration. For this purpose, self-locking nuts have a plastic insert or a more tightly cut thread. Such nuts can be used only once, otherwise the self-locking properties of the nut are lost.

Loosening Allen or Multi-Tooth Head Screws

When unscrewing both types of screws, you must clean the hole in the screw head from dirt before using the appropriate tool.

• Socket heads are best suited for unscrewing such screws.
• Unlike conventional curved wrenches (when using which the force always acts at a certain angle) the socket heads can withstand hammer blows from the square adapter side. By hitting the tool with a hammer or, in extreme cases, directly on the screw head, you can loosen the screw a little, making it easier to unscrew.

Loosening Phillips or Cross Head Screws

After a relatively short time, screws can sit so tightly that it becomes impossible to unscrew them with a single screwdriver. Unscrewing Phillips-head screws is further complicated by the fact that the screwdriver slips out of the slot even when pressing hard on the handle. After several unsuccessful attempts to loosen the screw, the Phillips-head slot is damaged, after which it is almost impossible to unscrew the screw.

• If the screw does not come out right away, place a suitable strong screwdriver against it and try to loosen it by hitting it hard with a hammer on the end of the screwdriver handle.
• In most cases, the screw, which often rusts only in the head area, will break loose and can usually be unscrewed in the usual way.
• If that doesn't help, use an impact driver. Each time you hit the top of the driver's handle, the driver will slightly rotate the socket head under pressure. This will remove almost any screw.

Drilling out self-tapping screws

If the screw head is in such a condition that it is practically impossible to use the tool, then the screw can only be drilled out.

• First remove the screw head using a drill bit of the appropriate size. If necessary, pre-drill the hole using a smaller drill bit.
• After this, the threaded part of the self-tapping screw can either be pushed through or pulled out from the back side with pliers.
• Otherwise, drill out the threaded part with a thin drill. If you choose a drill with a diameter that is too large, the hole for the screw will be so large that only a thick self-tapping screw can be inserted into it.

The screw falls off the tool

If you need to re-tighten a screw in a hard-to-reach place, you can prevent the screw from falling off the tool with the following simple trick: stick a small piece of chewing gum to the slot or tape the screw to the tool.

Loosening and tightening the expansion studs

Since the expansion studs do not have a surface to which a wrench can be applied, one must first be created.

• Screw tightly onto the free threaded part of the stud (counter) two nuts. Place a wrench on these nuts and loosen or tighten the stud.

Drilling out screws with stripped heads

The mating thread in which the screw with the torn off head protrudes should be damaged as little as possible.

• Use a center punch to strike exactly in the middle of the remaining part of the screw.
• Now you can drill. For screw sizes up to M8, you can do this immediately using a drill for a threaded hole. This is the diameter of a "shaved" screw, i.e. without the side of the thread profile. For screw sizes up to M6, the rule of thumb is: The diameter of the drill for a threaded hole should be equal to the thread diameter multiplied by 0.8. For example: thread M 6 x 0.8 = threaded hole diameter 4.8. For screws with a size of M8 and larger, the screw body must first be pre-drilled using a drill of a smaller diameter.
• The metal that remains in the threads can sometimes be removed with a scriber, but in most cases the threads must be driven with a tap.

Thread cutting

Threads cut in light metal are especially easy to strip, since in this case the material is not as hard as, for example, steel. If there is a lot of metal left, then you can cut a thread of a larger diameter. Otherwise, you will have to insert a threaded bushing, but this work should certainly be left to the workshop. Cutting the thread and running it with a tap is done in three stages. Therefore, the corresponding taps are called: roughing (one ring on the rod), semi-finished (two rings) and finishing (three rings or no rings) tap.

• Three taps are screwed in and then screwed out again, while the drilled hole is constantly lubricated with oil.
• To avoid stripping the tap, when screwing in the tap, you must constantly turn it back a little, otherwise the metal shavings become too long and jam.

Screw size and tightening torque

If screws and nuts are not subject to special loads, they are tightened using standard torques. Amateurs usually tighten screw connections by feel. So that you can use your torque wrench to check your feel when tightening screws and nuts, we provide torque values for the most common screw connections:

Thread diameter (mm)	6	8	10	12	14
Torque (Nm)*	10	25	49	85	135

*The torque values given do not apply to special screws or screws that are screwed into light metal.

(The full version is posted on the resource: AudiManual.ru)