Repair damaged threads with a helical thread repair kit

One of the most susceptible parts of damaging during periodic and repeated maintenance of an engine, or during successive repairs are threads, especially those practiced in the different parts of the crankcase, motor block and its elements. In modern engines, these threaded holes are usually manufactured directly on the component material (usually aluminum or steel alloy), and the screws that penetrate them as a general rule are of a harder material.
The insertion, tightening, loosened and posterior tightening of these screws usually gradually wear the thread, being softer, reaching extreme cases to spoil it completely and leave it unusable.

The problem and solution
When we face the problem of a thread with the spoiled threads, or “past” as it is commonly said we will no longer be able to correctly perform the determined tightening torque, because the screw will not have enough grip surface and turn if it exerts the necessary force to join the elements or perform their function.
We can choose to review the hole again with an "Threading male”Bigger, although we will also need and install a larger screw in diameter. The threading male consists of a very hard cutting tool that will create thread threads in the hole where it is used.

The problem is that we will not always be able to install a larger screw, since many times we will be limited by the characteristics and physical limits of the pieces (that is, it does not always "fit" a larger screw).
The other option, much more recommended is the installation of a helicail -like insert, and apart from allowing the installation of the original screw we will improve the original thread.

The Helicoil kit
The Helicoil Type Inserts They are a kind of reinforced steel dock, which is threaded in the spoiled hole and allows to create a firmer union, providing the following advantages:

-As allows us to use the original screw size.
-Reving the threaded, usually a helical thread is always stronger than a thread practiced in the block. In the same way, it eliminates stress and improves the accuracy of the tightening.
-Improves the quality and duration of the thread, it can even exceed the duration of the same screw.
The components of the Helicoil kit are the drill, the threading male, the inserts, and the installation tool.

How it is used
We are going to explain in a practical way how to repair a damaged thread using a helicail-type insert kit, in this case we have a fairly common example, where the thread of the clutch cable of a Harley-Davidson Sportster has deteriorated just where the cable is inserted In the primary chain cover, causing a small oil leakage through the hole.

After dismantling the lid and remove the cable we can visually check the damage to the threaded threads, which no longer allow the tightening properly.

The first step is to review the hole with the drill included in the kit, which will leave the right diameter for the next phase. Subsequently we will start the cut of the threads for the insert with the threading male, it is a critical step, you have to be very precise and go little by little, moving forward ¼ turn and unscrewing 1 return, in this way the remaining material will fall out of the hole and the thread will be of good quality.

Next we can enter the insert in the installation mandrel,

and helping us from the compression tool to thread gently until it enters completely in the hole.

The same insert acts as a brake when expanding, which will not get out when the screw unscrew.

The last step is to break the installation tongue of the insert,

If the hole is blind, we will do it by a dry blow with a botator, and if the hole is an intern as in this case we will simply cut the leftover with pliers.

Ending
We visually check that the insert is correctly located and we can already proceed to enter the clutch cable again, without forgetting to install a new O -O -ring to guarantee the tightness of the set, and we squeeze it at the indicated tightening torque: 4.1 to 6 , 8 nm.

With this we already have our repaired primary chain cover and our motorcycle again for the road.

By the way, if you need to repair the Harley-Davidson clutch cable, you can see the Helicoil kit HERE.

Frank Burguera

#mecanicaharley