Professional tips for mechanics (Fiesta 4)

Contents: Loosening a rusty fastener ↳ Unscrewing damaged nuts ↳ Unscrewing bolts with an internal… ↳ Removing slotted and Phillips head… ↳ Removing a fastener 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 off slows down and complicates the work. To protect yourself from such cases, we've provided some tips and tricks from professionals. A rusty threaded connection should definitely be replaced with a new one. This will ensure the necessary strength of the connection.

Loosening a rusty fastener

Before loosening a rusted nut or bolt, remove dirt and rust from the adjacent threads of the bolt. Otherwise, the friction on the ends of the threads is too great, and therefore the bolt is torn off.

Clean the free part of the thread with a wire brush and treat it with a rust neutralizer. If you use a fast-acting rust neutralizer, you can start unscrewing the nuts right away. If you use a regular neutralizer, you should wait a while before you start unscrewing the rusted fastener.

Use a wire brush to clean the threads, then spray rust remover onto the thread surface from an aerosol can.

If the rust remover works quickly, remove the nut immediately.

Other rust dissolving agents (oil, kerosene, diesel fuel, etc.) must be allowed to act on the rust for some time.

PRACTICAL ADVICE

Self-locking nuts

Self-locking nuts sit firmly on the thread and do not unscrew when vibrated. For this purpose, they have plastic inserts or slightly offset threads. Self-locking nuts are used only once; with repeated use, their locking effect deteriorates.

Unscrewing damaged nuts

If you have stripped the edges of a hex nut with an open-end wrench or rust has severely damaged the surface of the nut, only force will help to unscrew them.

Unscrew the nut, firmly grasping it with an adjustable (gas) wrench.

If this does not help, the nut is cut off with a sharp chisel. In such cases, auto repair shops often use a special device, the so-called "impact wrench".

In easily accessible places, the nut can be sawed along the thread with a hacksaw for metal.

Unscrewing bolts with an internal hexagon head or an internal "star-shaped" head

Before you begin to loosen the bolt, remove any possible dirt from the bolt head.

Long hex or star heads are best for loosening these types of bolts.

Unlike conventional open-end wrenches (where the force is always applied diagonally), the heads inserted into the adapter can also withstand a hammer blow. A blow - if necessary directly to the bolt head - often loosens the bolt and makes it easier to unscrew.

Removing slotted and Phillips head screws

After only a relatively short period of use, screws can rust so much that a normal screwdriver will no longer help. With Phillips-head screws, things are even more complicated: when you press hard on the screwdriver handle, the end of the screwdriver pops out. As a result, after just a few attempts, the Phillips slot is cut off and the screw is almost impossible to unscrew.

If the screw does not come off immediately, take a screwdriver with a strong handle and try to unscrew the screw connection by hitting the screwdriver handle with a hammer.

This is often sufficient, as most often the rust layer at the head of the screw is broken by a hammer blow, and after that the screw 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 screwdriver rotates. This tool can remove almost any screw.

Removing a fastener by drilling

If the bolt head cannot be removed with a tool, drilling will help.

First, drill out the head of the bolt with a large diameter drill. If necessary, you can first drill a preparatory hole in the center of the bolt head with a small drill.

A bolt without a head is knocked out either with a punch or unscrewed from the back side using pliers.

If this fails, carefully drill through the threaded portion with a drill bit smaller than the corresponding thread diameter and remove the remaining metal.

PRACTICAL ADVICE

Work in hard to reach places

If you need to tighten a screw in a hard-to-reach place, you can first secure it to the tool using body putty, chewing gum, viscous grease, or a strip of tape.

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 (lock). When unscrewing, the key grabs the lower nut, when screwing in, the upper nut.

Drilling out bolts with sheared heads

It is important to damage the threads as little as possible.

Use a center punch to mark the location for the drill in the center of the bolt remnants.

Drill out the bolt remains: for bolt sizes up to M8, you can use a drill to create a hole for the thread. The hole for the thread is the diameter of the bolt without the thread cut. For bolts up to M6, the rule is: the thread diameter is multiplied by 0.8. Example: threaded connection M6 x 0.8 = diameter of the hole for the thread – 4.8. Bolts with a thread size larger than M8 should be pre-drilled with a thinner drill.

Any metal residue remaining in the threads can be removed using a scriber or magnetic rod. However, in most cases, the threads will need to be re-cut.

Thread cutting

Since the light metal has less strength than steel, the threads are easily damaged. If there is enough metal around the old thread, you can cut a larger diameter thread. Otherwise, have the auto body shop insert a threaded sleeve in this place. Re-cutting the old thread or cutting a new thread is done in three stages. Therefore, the corresponding taps are called a roughing tap, number 1 (one ring on the neck), an intermediate tap, number 2 (two rings on the neck) and a finishing tap, number 3 (no rings or three rings on the neck).

The pre-drilled hole is constantly lubricated with oil. Starting from the rough, the taps are screwed in and out sequentially.

To avoid tearing off the tap, the cutting is done with slight forward turns (maximum 1/8 of a turn). Then the tap is turned back until the metal shavings break off, this prevents the tap from getting clamped in the hole.

TECHNICAL DICTIONARY

Bolt sizes and tightening torques

Standard tightening torques are sufficient for normal bolts and nuts. When tightening simple fasteners, experienced mechanics feel the tightening torque by hand. If they do not trust this feeling, they use a torque wrench. The following tightening torques correspond to the most common bolted connections: