Gap between electrodes of spark plugs: measurement, adjustment

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:42

The operation of an internal combustion engine largely depends on the condition of the spark plugs. They are responsible for the timely ignition of the fuel mixture in the chambers. Therefore, the slightest malfunction of at least one of them will inevitably lead to the fact that the engine starts to triple or even stall. This article will focus on such a concept as the gap between the electrodes of spark plugs. We will try to find out what it affects, what it should be, how it can be adjusted independently.

What is a gap?

Any spark plug of an automobile internal combustion engine has two electrodes in its design: central and side. The first one is positive. It is on him through the contact tip, the rod and the conductive sealant (resistor) that the high voltage current generated by the coil is supplied. The side electrode is negative. It is welded to the body of the device and closes to ground through the thread and the skirt of the candle. A spark is nothing more than an arc discharge that occurs between electrodes. It slips during the supply of an electrical impulse created byignition coil. Its size and power directly depend on the relative position of the electrodes, that is, on the distance between them, called the gap.

What affects the clearance?

For each type of engine, depending on the type and octane number of fuel consumed, volume, developed power, pressure in the combustion chambers, car manufacturers provide different candles with different characteristics. In other words, simply taking and rearranging them from the Mercedes to the Lada will not work in any way. The gap between the electrodes of the spark plugs is their most important characteristic, which determines the stability of the engine, its power, the number of revolutions developed, fuel consumption, and the durability of the parts of the piston group.

Reduced clearance

The reduced gap between the electrodes of the spark plugs is characterized by a powerful but short-term spark discharge. Reducing the time leads to the fact that the fuel mixture does not have time to burn out completely. As a result, the candles are flooded with the remnants of fuel, the spark periodically disappears, the engine troit. Naturally, fuel consumption also increases. The amount of toxic substances in the emission is also increasing sharply.

Such a phenomenon at high speeds often leads to the fact that the spark, being too short, does not have time to break between incoming electrical impulses, forming a constant arc. As a result, we can get burnt or completely melted electrodes, as well as an interturn circuit in the coil. Complementing this picture is the difficult start of the engine andaccelerated wear of piston group parts.

Increased clearance

Increased gap between the electrodes of spark plugs, on the contrary, leads to the fact that the spark lengthens, but becomes too weak to ignite the combustible mixture. In addition, the probability of breakdown of the coil, high voltage wire or insulator increases. With too much distance between the electrodes, it is easier for electricity, which by its nature takes the shortest path to equalize the potential difference, to pass through the ceramic than to overcome the increased gap through the air. As a result, the spark in the cylinder either forms periodically, or disappears altogether. At the same time, the engine chokes on fuel, troit or stalls. A characteristic phenomenon for increased clearance is rare loud pops caused by misfiring.

What should the spark plug gap be?

As we have already said, the distance between the electrodes of the spark plugs is different for each engine. Owners of modern foreign cars do not have to think about such a thing as a gap. Everything is simple here. There is an engine - there are certain candles for it with a certain distance between the electrodes. And the manufacturers of foreign cars categorically do not recommend their self-adjustment.

It's a little more complicated with our cars. The gap between the spark plug electrodes for domestic cars can be from 0.5 to 1.5 mm. First of all, it depends on the type of engine. For carburetor engines with contact ignition, for example, the gap varies from 1up to 1.3 mm, and with contactless - 0.7-0.8 mm. For engines with automatic injection, manufacturers recommend the distance between the electrodes within 0.5-0.6 mm.

Why check clearance? How often should this be done?

You ask: "Why check and adjust the gap, if you can buy the recommended candles, install and forget about them until the end of the prescribed period of work?" The fact is that during the operation of the engine, the electrodes burn. As a result, the distance between them increases. Because of this, it is recommended to check single-electrode candles at least every 10-15 thousand kilometers, multi-electrode - after 20-30 thousand km.

How and how to measure the gap?

Determine the distance between the electrodes will help a special probe for measuring gaps. You can buy it at any store specializing in the sale of auto parts. The only thing you should pay attention to when buying it is the manufacturer. Do not purchase a measuring tool of dubious origin and quality. Hundredths of a millimeter deviation can negate all your efforts to adjust the gap. There are three types of test probes:

• coin-shaped;
• wire;
• plate.

The first gap gauge looks like an ordinary coin with a rim around it. It has different thickness at different positions of the circle. At the same time, a scale indicating its value is applied on the “coin” itself. The wire probe hasa similar design. Only instead of the rim, the role of the meter is performed by loops of wire of different diameters. The most popular tool for measuring clearance is the Swiss Army Knife Gauge. Here, instead of blades, steel plates of a certain thickness are used.

How is the gap determined?

First of all, the candle must be cleaned of dirt and soot, which may be present on its contacts. The measurement method for each type of probe is different. If you have a coin-shaped meter, place its rim between the spark plug electrodes. Slowly turn it until it connects the contacts. Now look at the "coin" scale. The value printed on it at the location of the electrodes will be the size of the gap. To increase it, simply bend the side contact with the rim of the gauge and check the distance again. To reduce the gap, the electrode should be slightly bent, resting it on some immovable object.

If you have a wire probe, measurements are made by placing a wire loop between the contacts. Each of them has a certain diameter. The thickness of the loop, which will block the distance between the electrodes, will be the gap. The bending of the side contact is carried out with the help of special curly plates located on the body of the wire probe. It is easiest to check the gap with a plate gauge. It is enough to pick up a plate that fits snugly between the electrodes, and look at its thickness, indicated on itssurfaces. Gap adjustment is also performed using the meter itself.

What should be the gap between the electrodes of spark plugs on gas?

All car owners whose cars are converted to HBO are wondering which spark plugs are best suited for this type of fuel and what should be their distance between the electrodes. Indeed, the process of combustion of the gas-air mixture occurs a little differently than the air-fuel mixture. First, propane has a high octane rating (105-115). Secondly, its combustion temperature is about 30-50 degrees higher than gasoline. Thirdly, a higher compression ratio in the cylinder is needed to burn the gas.

In other words, if the engine of your car is designed for the 80th or 92nd gasoline, when running on HBO, ordinary candles will fail very quickly. In addition, the engine of the machine will constantly overheat, and the parts of the piston group will wear out quickly. To avoid this, it is necessary to use candles with a minimum glow number provided by the car manufacturer. If the car's engine is configured for gasoline with an octane rating of 95 or higher, the conversion to gas will not affect it in any way. As for the gap, it should be as recommended by the manufacturer.

Design features of some spark plugs

Modern technology allows manufacturers to produce spark plugs with improvedcharacteristics of the power and size of the electric spark. This can be achieved through the use of precious and rare earth metals. Each of the manufacturers is trying to find the ideal design option, in which the spark will be as powerful as possible, and the gap will be large. Candles Denso, NGK, Bosch, Champion, despite the high cost, are in great demand because of their reliability and durability. So how are they different from regular ones?

Take Denso spark plugs for example. Their electrodes are made of iridium, and the central contact has a diameter five times smaller than that of conventional candles. "What does it give?" - you ask. First, this metal is very resistant to high temperatures. Secondly, if you are using iridium spark plugs, the gap between the electrodes allows you to create the largest possible spark. So you will not only increase engine power, but also reduce the amount of harmful impurities in the exhaust. And thirdly, they will last twice or even three times longer than usual.