What Gap Should Be On The Spark Plugs?

Even after purchasing and installing a new set of candles, various troubles sometimes occur. The work of the engine may be uneven, and there are jerks, as well as detonation. Not everyone knows what the gap should be on the candles. It is necessary to correct this gap, and the motor will work again, as expected.

What it is?

This gap is the distance between two electrodes. It is necessary for optimal ignition of the fuel mixture and the normal operation of the candle itself. If this distance is even slightly different from the standards recommended by the manufacturer, then you can forget about the smooth operation of the engine. The car twitches during acceleration and uniform motion, and detonation are also observed.

Ignition work in the combustion chamber.

Candles are the last element in the ignition of the car. They are constantly in direct contact with a mixture of gasoline and air. Candles and ignite the combustible mixture. And ignition can be effective, as it should be according to the technical regulations and ideas of engineers, or with low efficiency due to the influence of certain factors.

After the fuel-air mixture hits the engine cylinder, the piston will go up. Thus the mixture is compressed. At the moment when the piston reaches its peak or dead center, the Hall sensor or ECU gives an impulse or command. As a result, the mixture is ignited. A candle is responsible for ignition. an electric spark jumps between its two electrodes, which provokes the burning of the fuel mixture.

But this burning may not be. It is not necessarily due to any malfunction in the ignition system. Just set the wrong gap. So, misfire may occur, due to which engine efficiency is significantly reduced. Sometimes the engine may not start at all.

The effect of spark gaps on engine performance.

Let’s look at how the gap between the spark plug electrodes will affect the engine performance. It is an important parameter that should be considered when diagnosing a power unit.

Small clearance.

In the case where the gap is insufficient, you can observe gaps in the process of ignition of the air-fuel mixture. The spark that forms between two electrodes that are close to each other is too weak to ignite a combustible mixture. It may even be strong enough, but not enough to maintain a stable burning.

Therefore, cars can twitch when driving, slowly pick up speed, do not develop full power. In the carburetor power supply system, candles are often filled with fuel too. the engine will troit. You can solve the problem by increasing the gap in the candles.

How to understand that it is small? Speaking of size, the gap can be 0.1-0.4 millimetres. It is important immediately after purchase to check the distance between the electrodes and, if necessary, adjust it.

Large gap candles.

Most candle manufacturers set normal clearances. However, during operation, the distance between the electrodes may increase. The gap does not grow by itself, but due to wear. It manifests itself if the candle works long enough. The electrodes are metallic, and they have to work under the influence of discharges and high temperatures. Over time, these elements fade. In this case, both electrodes suffer. upper and lower. The first is made more subtle, rounded. And the second goes down.

For this reason, the power of the spark drops, and quite significantly. A significant gap in the candles also can not normally set fire to the fuel mixture. For this very reason, breakdowns to the insulator of the lower electrode often occur. The spark will surely find the shortest way for itself. In winter, the car may not start at all.

It should be noted another important point. On electrodes, the gap of which is too large, carbon is more often formed. The spark suffers from a large gap, and here it is also a dense black patina. The ignition on such a candle may not pass at all. It is important to turn out the candles and change or clean them periodically. It is recommended to do this every 15 thousand kilometres. A large gap is a distance between the electrodes of 1.3 mm or more.

What is the norm?

What gap should be on the candles, if the lower limit of 0.4 mm, and the top. from 1.3 mm? The optimal parameter for each motor will be different. First of all, different gaps are needed based on different ignition systems. For injection engines, the normal clearance can be considered a distance from 1 to 1.3 mm.

For carburetor engines, where the ignition is operated based on the distributor and the Hall sensor, the distance between the electrodes from 0.5 mm to 0.6 mm is considered normal. If the ignition is electronic (and this is not uncommon on modern cars), then the gap on the spark plugs of the VAZ-2170 should be in the range of 0.7 to 0.8 mm.

As you can see, the difference is quite significant. It’s all about different ignition systems. Carburettor cars have low voltages, and the spark here will be weaker. Accordingly, the gap should be minimal.

On injection engines, the ignition is more powerful. High voltages characterize the electrical system. That is why the normal spark plug clearance for the injector is larger. If the distance is less, the motor will not work stably.

Check and set clearance.

To measure the gap is straightforward. First, they need to unscrew, clean, and then take measurements. It is best to use a measuring probe to measure the gap. But if it is not, you can do with a regular ruler.

Adjustment is also straightforward. with a smaller gap with a screwdriver or something else pushing the electrodes apart. If the distance is greater, then you can knock on the top electrode with something.


If the engine is unstable if there is a misfire if it seems that the engine troit, first of all, it is better to check what the gap should be on the candle. The resource and serviceability of the engine operation depend on it.