The engine is a device that generates energy by igniting and exploding the compressed mixture in the cylinder, and the ignition element in the combustion chamber is the spark plug. Under the condition that the compressed air pressure in the combustion chamber is very high and it is not easy to produce electric sparks, whether the ignition is reliable or not has a great influence on the starting performance, fuel consumption, acceleration performance and high running durability of the engine. Because the spark plug works under extremely harsh conditions of high temperature, high pressure and high impact force, it must have high temperature resistance and high strength. This requires drivers to have a basic understanding of spark plugs, correctly select spark plugs and maintain them in time to keep your car in good technical condition.
First, the structure of the spark plug
Spark plug is generally composed of center electrode, side electrode, threaded part, insulator, spark plug shell, connector, gasket and so on.
Center electrode: the electrolytic part located in the center of the spark plug. The electric energy of the high-voltage line is transmitted to this part, and the gap between the electrodes on the same side produces sparks. The electrode of high performance spark plug is made of finishing and platinum welding. In order to quickly discharge a large amount of heat energy, some spark plugs have copper plates installed in the insulator of the center electrode.
Side electrode: The side electrode is an electrode connected to the threaded part of the spark plug and grounded through the thread. The high-performance spark plug also cuts a very thin groove on the surface of the side electrode, which makes it easier to generate sparks.
Threaded part: The threaded part is mainly used to fix the spark plug and support the side electrode, and also has heat dissipation function. Different types of spark plugs or the same spark plug are used in different engines, and their thread diameters and thread lengths are different. Therefore, the same spark plug will be classified according to different models.
Insulator: Insulator not only has supporting performance, but also can prevent the leakage of electric energy. Between the connector and the spark plug housing, in order to extend the insulation distance and reduce the influence of dust and moisture on leakage, the insulator is designed as a folded skirt.
Gasket: The main function of gasket is to make the spark plug and cylinder have a good seal when tightening the spark plug. When the same spark plug is screwed on and removed repeatedly, the sealing effect of the gasket will be weakened. The electrode part of spark plug is the focus of use and maintenance.
The end shapes of the center electrode and the side electrode and the gap formed between the two electrodes are important factors affecting the ignition of the spark plug. Therefore, when judging whether the spark plug can be used, first visually check whether its shape is intact and whether the gap is appropriate. Generally speaking, the gap of spark plug can be measured with a thickness gauge.
Second, the thermal characteristics of spark plugs
Spark plugs can be divided into three types according to different thermal characteristics: cold type, warm type and hot type. Cold spark plug insulation skirt is short, the heating area is small, and the heat dissipation distance is short, so it is equal. In this case, the working temperature of the cold spark plug is low. Thermal spark plug insulator skirt is longer; Large heating area, long heat dissipation distance and high working temperature. The working temperature of a warm spark plug is between that of a cold spark plug and a hot spark plug.
In the product models of spark plugs, the thermal characteristics of spark plugs are usually expressed in Arabic numerals. The number indicating the thermal characteristics of the spark plug is called the calorific value of the spark plug.
The calorific value is a relative comparison value of the thermal characteristics of spark plugs. Among the models of spark plugs in China, NGK spark plugs and Japanese nd spark plugs, the heat value of cold spark plugs is larger. Thermal spark plugs have a low calorific value. In other words, with the increase of calorific value, the thermal characteristics of spark plug gradually cool down from heat.
Third, the use and maintenance of spark plugs
The spark plug allows sparks to splash into the gap between the center electrode and the side electrode; In the process of spark splashing, the corners of the center electrode will peel off to form a band-shaped circle, which will gradually expand the gap and reduce the ignition performance. In short, spark plugs are consumables and must be maintained regularly. Motorcycles must be replaced with new products every 3,000-5,000 kilometers. The function of the spark plug is to generate a breakdown spark between the side electrodes through the electric energy from the high-voltage conductor. The materials and shapes of the center electrode and the outer electrode, as well as the gap between the two electrodes are the most important parts that affect the spark generated by the spark plug, so it must be fully understood before maintenance.
1. Keeping the electrode clean can maintain the ignition performance of the spark plug. In actual maintenance, the spark plug needs to be removed. Because of the different shapes of motorcycles, it is sometimes necessary to remove the fuel tank, especially the motorcycles produced in recent years, whose fuel tank is equipped with many oil hoses and wiring; So we have to get rid of it together. When assembling, be sure to confirm whether the oil hose and line are assembled in the original position.
Spark plugs are consumables, and regular maintenance can prolong their service life. In addition, before the replacement period, the performance of the spark plug will be inhibited. As for the method of maintaining life, the first is cleaning, that is, cleaning the carbon deposits attached to electrodes or insulators. Because the carbon deposit is a conductor, when the carbon deposit is attached to the spark plug, it will weaken the leakage or splash sparks, and the original cooling effect cannot be exerted due to the influence of carbon deposit; In order not to damage the spark plug when cleaning it, you can clean it with a copper brush.
2. electrode shape renovation and electrode gap adjustment with the increase of service time, the shape of spark plug electrode and its gap will change. Especially for the center electrode, after continuous spark splashing, the surface will become rough and the corners will peel off, which makes it difficult for sparks to splash. Therefore, it is necessary to use a drop knife for shaping, in order to present the original smooth surface and complete corners. Therefore, the gap between the electrodes will become larger, which needs to be measured with a thickness gauge and adjusted to the original prescribed gap. If you can do the above regular maintenance, you will be sure to keep the spark plug in good technical condition.
3. The judgment of spark plug fault
It is very important to repair the spark plug, and the key point is to check the combustion color of the electrode, from which the engine operation can be judged.
(1) Check the ablation color of the electrode.
It can be judged whether the working state of the engine is normal from the combustion color of the electrode. Spark plug has self-cleaning function in a certain working temperature range; If the spark plug with specified calorific value is used, the electrode part turns yellow brown, indicating that the spark plug works in the normal temperature range; If the electrode turns cold white, it means excessive combustion.
Of course, the situation of spark plug combustion is closely related to factors such as season, temperature and driving conditions. If there is a cold white ablation color, use a spark plug with a calorific value less than the specified spark plug. If there is carbon deposit; Consider using spark plugs with high calorific value. Of course, at the same time, we should also consider the problem of mixing ratio, and determine which spark plug is better while correcting it.
If the spark plug turns black, generally speaking, the combustion temperature is too low, because the mixture ratio of the mixture is too rich. There are many reasons why the mixture thickens; But the main reason is that the air filter is not clean, which leads to insufficient air intake and makes the mixture rich. Therefore, we should also start to purify the air and remove oil. If the spark plug turns white, this overheating combustion phenomenon is caused by too high combustion temperature. This is because the intake system such as intake manifold is loose and cracked, and secondary air is sucked, or the exhaust system leaks air, which makes the mixture dilute. Therefore, the related parts of carburetor or exhaust pipe should be inspected and repaired.
(2) Check whether the electrodes of each cylinder are completely burned.
For multi-cylinder engines, except for special circumstances (such as different combustion conditions or cooling conditions of cylinders), the combustion color and spark plug color of each cylinder should be basically the same. Therefore, by comparing the combustion colors of spark plugs in each cylinder, it can be judged whether the engine is running normally. During inspection, the spark plug of each cylinder must be removed and then inspected side by side.
(3) Check the electric spark
Before assembling the spark plug. Be sure to check the electric spark, that is, to confirm the ignition of the spark plug. When the ignition system (including spark plug) fails, we can judge which part is out of order after checking the spark, and find out the reason why the engine can't start. If you can't get in and out of the spark plug, you can install another spark plug and check the spark. If there is something wrong with the spark plug itself, it is of course impossible to get in and spark. If not, then it must be; There is something wrong with the high voltage in front of the spark plug. During operation, it is necessary to check whether the side electrode is deformed for the grounded spark plug. If so, under the condition that other parts are not damaged, the side electrode can be pried open with a screwdriver and restored to its original state.
4. Matters needing attention when assembling spark plugs
(1) When assembling spark plugs, align the threads before screwing them in, screw them in by hand, and then tighten them with a spark plug wrench. However, do not use too much force when tightening the spark plug. Generally speaking, when screwing in a new spark plug; It is suitable when the gasket begins to deform. Usually, beginners don't notice this. Therefore, when repairing the spark plug, the thread of the spark plug is often damaged. Tighten the spark plug correctly.
(2) Because the high-voltage line is plugged into the spark plug cap, if there is no problem with the spark plug, there is no spark in the high-voltage line test and there is no spark after the spark plug is connected, then the high-voltage line is not plugged in or the resistance in the spark plug cap is not screwed on (or the resistance is bad). When the high-voltage wire is not in good contact, you can cut off a short section of its head and clean the rust on its surface, and then insert it into the spark plug cap.
(3) When assembling, check whether the high-voltage line is aging or cracked, because the aging high-voltage line will leak electricity in rainy days or splash water, which will affect the ignition of the spark plug. Aging high-voltage lines should be updated.