What to do before changing the spark plugs

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In this article Chica Mecánica explains what to do before changing the spark plugs of our car and how to know if they are damaged.

Considerations to take into account to change the spark plugs

Hello that, here I leave another article about the things that should evaluate before changing the spark plugs, because often with a single cleaning they are almost like new addition with some maintenance we can extend the life of them.

Really searching again on the internet I did not get good information about the subject, and what I got is very scattered so I decided to write this article with the excerpts from other articles in a way that is more like a reference guide for the subject.

Inspection procedure for the spark plugs.

1.- First of all, once the engine spark plug is removed, it must be inspected.

It is important because it gives us valuable information about how the machine is working and then I show you an image that abounds on the Internet of the state of the spark plugs and their meaning.

estado de las bujias

2.- Measure is the distance between the central electrode and the ground electrode.

This should be between 0.7mm and 1.1mm for normal standard cars. If it is not in that size (due to the use both electrodes wear out), you can give small blows to the ground electrode so that it reaches the aforementioned distance. The mass electrode can not be bent too much, it could break inside the cylinder causing damage.

It is important to take them to the correct separation so that the spark delivers the highest caloric energy to the mixture without overloading the ignition coil. Read more about it in my article about spark plugs

Another important thing before making the adjustment is that both electrodes should be free of soot, usually if the engine is working with very rich mixtures will form crusts of ash that deteriorate the spark. Usually with a good wire brush it is possible to remove these impurities. Note that this is only possible for normal nickel or copper spark plugs.


3.- External cleaning of the spark plug.

All spark plugs "except the electrode coated" can be cleaned, either mechanically with a wire brush, ultrasound or scraped with a tip. You can also use chemical solvents such as tiner or cleaner carburetor. I usually use both methods.

It is important to note that when cleaning the insulator is as white as possible. If it remains dark brown or black after cleaning it means that the ceramic has a lot of impurity and we run the risk of the spark going through the insulator. This phenomenon is called a communicated spark, and is characterized by the fact that the spark exists, but it is not seen, so it has very little caloric content and the mixture will not burn in the engine.

bujia comunicada dañada

The only way to repair these spark plugs is with a more thorough cleaning with ultrasound, but it is a matter of evaluating the cost benefit. How is that? Well, if the electrodes are badly damaged it's not worth spending for cleaning if the spark plug does not have a lot of life left.

When to replace the spark plugs?

1.- If the ceramic of the insulator is split.

2.- If the wear of the central and mass electrodes is excessive and it is no longer possible to do the recalibration or if doing the same implies a risk of detachment of the mass electrode.

3.- If the dirt can not be removed from the central electrode with the methods described above.

4.- Expiration of its useful life. In my opinion, more than 70 thousand km for a spark plug is more than enough to relieve her of her position. Many will say that 70 thousand kilometers is crazy, but believe me that with a good routine of maintenance where every 10 thousand kilometers are cleaned, recalibrate can reach that number without problems with normal spark plugs.

Errors when choosing or cleaning the spark plugs that we should avoid

The most common errors are:

1.- Choice of spark plugs of inadequate thermal grade.

Of course, if we have a car that travels a lot on motorways at high RPM the choice of a cold spark plug is the best option, but if the machine already has a good mileage track, the wear and presence of oil in the combustion chamber is a problem, we can replace it with a higher thermal grade so that the soot remains burn as much as possible.

If we choose a spark plug of high thermal grade and place it in a high-performance motor, we run the risk of overheating and melting. Which would be terrible for our engine.

2.- Inadequate thread length.

This is more than understood.

If it is very long we can damage the piston, problems of plaque formation in the thread that prevents the exit of the same and overheating of the spark plug.

If it is very short, we will have problems of poor inflammation of mixture and insufficient temperature to burn waste.

3.- Handle the sealed seat of the spark plug

In the case of spark plugs with a conical watertight seat, no washer or gasket should be used.

Spark plugs with a flat watertight seat use only the "safety" gasket installed. This seal must not be removed or replaced by a washer. Without the gasket, the spark plug penetrates too much into the combustion chamber, which disturbs the passage of heat from the body of the spark plug to the cylinder head, and the seat ceases to be leakproof, furthermore thermal expansion and contraction produces the spark plug Stick to the camera.

If an additional gasket is used, the spark plug does not penetrate sufficiently into the threaded hole, and the passage of heat from the body of the spark plug to the cylinder head is also reduced.


If you want to know more about the spark plugs, you can visit my article in this link.

Well, cheer up! that, if you have dirty spark plugs, there is no need to throw them away, they are cleaned and they go back to work perfectly and without problems. We help the environment by reducing polluting gases due to bad combustion and we avoid the spark plug waste that still works with a little love.

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Written by:

Dennis García

Mechanical Girl





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    What to do before changing the spark plugs

    What to do before changing the spark plugs

    In this article Chica Mecánica explains what to do before changing the spark plugs of our car and how to know if they are damaged.

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    • Asked by Edgar Lavado R
      on 04/21/2018
      Gracias Dennis por tus recomendaciones. Quisiera saber que nos dices respecto a: 1,- Cómo elegir el grado térmico de las bujías, en motores de 1300 cc 4Cil. gasolina. 2.- Qué criterios aplican y si existe una tabla o referencia que se pueda conseguir. 3.- La longitud del cable, resistencia, construcción y condición. Su relación con el calor generado. 4.- Octanaje o rango de calidad de la gasolina que puede condicionar la saturación de energía para el "salto" de la chispa. 5- El caso de bujías con más de un electrodo y calibraciones. Answer:
      Que tal Hector, yo escribí un articulo mas o menos con los temas que planteas e http://www.intarcesoft.com.ve/es/automotriz/acerca-de-las-bujias.html. El grado térmico depende del fabricante del motor y el uso que le des al motor, no se si exista alguna tabla para ello. La resistencia de los cables mas que todo esta para reducir la interferencia y en sistemas DIS obliga a la chispa a salir por donde es requerida, no modifica el grado térmico. Algo parecido pasa con las bujías de varios electrodos, lo unico que obtienes es confiabilidad y durabilidad en función del envejecimiento. Es decir, no hay diferencia entre una bujía nueva de un solo electródo con una de multiples. La diferencia se nota a medida de que va envejeciendo la bujía, debido a que por la cantidad de electrodos siempre habrá un camino para una buena chispas, caso que no pasa con la de un solo electrodo en donde solo hay un camino.
    • Asked by Bernardo
      on 10/25/2018
      Buenas.. Quisiera saber que tipo de bujias son las indicadas para un Chery Orinoco, si hay alguna marca en especial o numeración determinada para que funcione de manera óptima. Answer:
      Las bujias recomendadas son las K7RTP.

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