Techniques of a mechanic (Mercedes-Benz E-Class W210)

Contents: Unscrewing rusty fasteners ↡ Unscrewing damaged nuts ↡ Loosening bolts with an internal…↡ Unscrewing slotted and cross-head…↡ Removal fasteners by drilling ↡ Unscrewing the studs ↡ Drilling out bolts with sheared heads ↡ Thread cutting ↡

A nut that won't come off or a bolt head that's stripped will slow down and complicate the job. The following tips will help unskilled mechanics deal with these problems. Rusted fasteners should always be replaced with new ones. This will ensure the necessary strength of the connection.

Unscrewing rusty fasteners

Before you apply a wrench to a rusted nut or bolt, remove any dirt from the visible free threads of the bolt. Clean the free threads with a wire brush and treat with a rust neutralizer. If you are using a fast-acting rust neutralizer, you can start loosening the nuts immediately. If you are using a regular neutralizer, you should wait a while before you start loosening the rusted fastener.

Self-locking nuts sit firmly on the thread and do not turn away even due to vibration. For this purpose, they have inserts made of artificial material or narrow threads. Self-locking nuts are mainly used once, otherwise their effect disappears, so always replace removed self-locking nuts with new ones.

Unscrewing damaged nuts

If you have knocked off the edges of the nut or they are badly damaged by corrosion, then only force will help you unscrew them. Try the following:

unscrew the nut, firmly grasping it with adjustable pliers (with a gas wrench);
if adjustable pliers don't help, use a sharp chisel and split the nut;
if convenient, cut the nut along the thread with a hacksaw for metal;
if there is enough space near the nut, use a nut splitter. The bolt of the tool is tightened until the nut splits. The advantage of this method is that the threads of the bolt are not damaged;
use the so-called "nut breakers" which are used to loosen nuts at stations.

Loosening bolts with an internal Allen head and a "star"

Remove any dirt from the bolt grooves before inserting the appropriate keys.

Article text obtained from the website www.mercedesman.ru

It is best to use long hexagonal or, respectively, "star-shaped" heads for unscrewing such bolts. As opposed to conventional open-end wrenches (in which the force is always applied to two sides of the bolt) the push-on heads transmit force to all edges. Hammering the tool (or, in extreme cases, directly on the bolt head) will loosen the bolt a little, making it easier for you to unscrew it. A hammer with a copper or artificial head will not damage the part, but will affect the bolt like a regular hammer.

Work in hard to reach places

If you need to install and tighten a bolt in a hard-to-reach place, use the following methods. To prevent the bolt from falling out of the tool, stick a little chewing gum or apply thick grease to the head of the bolt and insert it into the key slot or attach the bolt to the tool with adhesive tape.

Unscrewing slotted and cross-head screws

After some time, the screws can become so rusty that they can no longer be removed with a simple screwdriver. With Phillips screws, even with not very strong pressure on the screwdriver, after numerous attempts, the Phillips slots can be damaged so much that it will be impossible to remove the screw.

If the screw cannot be removed immediately, do the following:

take a strong screwdriver that is exactly the right size for the screw and try to loosen the screw connection with a strong hammer blow on the end of the screwdriver handle. Often the screw is heavily corroded only at the head, so after a hammer blow it can be easily unscrewed;
if this does not help, use an impact screwdriver. Each time you hit the back of the impact screwdriver handle with a hammer, the working part of the impact screwdriver rotates. This tool allows you to unscrew almost any screw.

Removal fasteners by drilling

If the bolt or nut cannot be unscrewed using the above methods, then only drilling will help, which you do as follows:

use a large drill to drill out the head of the bolt. If necessary, you can first drill a preparatory hole in the center of the bolt head with a small drill;
either knock out the remaining threaded part or remove it with pliers;
if this fails, carefully drill through the threaded portion with a drill bit smaller than the corresponding thread rating and remove any remaining metal from the mating portion.

Unscrewing the studs

Since the studs cannot be unscrewed with a regular tool, do the following:

screw two nuts one after the other very tightly onto the free threaded part of the stud (counter);
use a wrench to grab the bottom nut and unscrew it together with the stud.

Drilling out bolts with sheared heads

The thread in which the bolt with the sheared head sits should, if possible, not be damaged, for which:

punch the center of the remaining bolt;
now you can start drilling. Bolts up to size M8 can be drilled with a drill for a threaded hole (this is the diameter of the bolt body without threads). For bolts up to M6, the rule of thumb is to multiply the thread diameter by 0.8. For example: threaded connection M6 x 0.8 = thread hole diameter = 4.8 mm. Bolts of size M8 and above should be pre-drilled with a thinner drill;
remove any remaining metal particles from the threads with a scriber. However, in most cases, the threads will need to be re-cut.

Thread cutting

Threads cut in light metal are especially easy to tear out, since their strength is not as high as that of steel. If there is enough metal, you can make a larger diameter thread. Otherwise, you should use a threaded bushing - this work is carried out at a car service.

Thread cutting is performed in three stages using appropriate taps of numbers 1, 2 and 3. When performing this work, constantly lubricate the hole for the thread with oil. In order not to knock down the thread, it is necessary to cut it carefully, applying a small axial force to the tap, periodically unscrewing it and then screwing it in deeper. Upon completion of the work, clean the thread from remaining metal chips and additives.

Fastener sizes and tightening torques

Bolts and nuts that do not have special tightening requirements are tightened with a standard torque, which depends on the diameter of the bolt (nut) thread. Most amateur mechanics tighten them "by feel". The dependence of the tightening torque on the thread diameter is as follows: