What Gap Should Be On The Candle? Spark Plug Clearance Adjustment.

At the moment, there are several types of internal combustion engines. gasoline and diesel. And if for the work of the latter the arson of the mixture is not required (it burns on the force of compression), then in the case of gasoline a spark is needed. It produces a special element. a candle. Those are available on injection and carburetor machines. When operating, motorists often wonder what the gap should be on the candles. Today we will talk on this topic in more detail.

About the work of ignition.

A candle is the last element in contact with the fuel/air mixture. Its main function is the burning of fuel at the moment when the piston is in the top dead center. Voltage is supplied from high-voltage wires. In turn, the interval between the spark supply is set by the ignition coil. When the piston is at TDC, a spark runs between the electrodes of the spark plug. She is a catalyst for this process.

The mixture is ignited, the compression energy is transferred to the piston. After the exhaust gas process is repeated. However, for the spark to be able to penetrate the electrodes normally and ignite the mixture, the gap must be optimal. During operation, it changes. So, distinguish between small and large gaps. How they affect the operation of the engine, we will tell further.

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What does a small gap affect?

If the gap between the electrodes is small (less than 0.4 millimetres), first of all, it will be manifested like the engine operation. In this case, the owner will observe omissions in the ignition. Why is this happening? The fact is that for the burning of a combustible mixture, a powerful spark is required. And since the distance between the electrodes is small, then its strength will be negligible. As a result, the combustible mixture will ignite through time. The motor starts uneven combustion process of the fuel-air mixture. On the carburetor units often “floods” candles. It is not very good since the motor operates in overload mode.

Big clearance is not always good.

Therefore, if the spark is weak with a small gap, it should be maximized. But it is not so. If the gap is 1.3 millimetres or more, the spark will not pass between the electrodes. The motor starts uneven combustion process of the fuel-air mixture again. In addition to this, carbon deposits will appear on the candles.

How often to check?

Note that the manufacturers themselves do not oblige to check and adjust the clearance (including iridium candles). However, practice shows that over time, this parameter automatically changes in one direction or another, since the candle is constantly under voltage and high pressure. What to do in this case? Experienced motorists recommend checking the gap on the spark plugs every 15 thousand kilometres and, if necessary, correct the readings.

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What gap is normal?

So, we have certain data. A small gap is all that is below 0.4 millimetres. Large. 1.3 and higher. What gap should be on the candles? It all depends on the type of food. On carburetor cars with a distributor ignition system, this parameter is 0.5-0.6 millimetres. But not all units should be such a gap in the candles. The carburetor with electronic ignition works fine with a gap of 0.7-0.8 millimetres.

Spark plug for gas.

How to set?

If you notice that the car began to behave differently, misfires appeared, it is worth checking the condition of the candles. Perhaps they have the wrong clearance. To correct the parameter, disconnect the high-voltage wires and unscrew the spark plug with a special key (as in the photo below).

So, go to the setting. Using probes, we determine the exact clearance on the spark plugs. Please note that on vehicles with a contact system (the old “Lada” and “Muscovites”), this parameter is 0.1 mm lower than on contactless ones. If the gap is less than usual, the electrode is bent over with a flat screwdriver. If the value is higher, the element is pressed with the same tool, only on the other side. Some candles may have a lateral arrangement of the electrode (and there are several).

In this case, the gap is set for each element. Takeoff should be minimal. Having set the gap of one candle, we twist it into place, put the armour wire and proceed to set up the next one. It is important not to confuse the location of high-voltage wires. Therefore, twist the candles alternately, and not all at once. Or make special tags. Otherwise, the engine may not start. At this stage, the setting of the spark plugs can be considered complete.

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Why is it important to stick to the norm?

A properly adjusted candle is not only a guarantee of well-coordinated engine operation. The gap parameter also affects fuel consumption. By setting the desired distance between the electrodes, you will reduce it by 5-6 percent. Also, a normal gap has a positive effect on the resource of the candle itself since it will no longer break through the insulator.

If you regularly monitor this parameter, the resource of a candle can reach 60 thousand kilometres. It applies to both injection and carburetor engines.


So, we figured out what the gap should be on the candles, and how to adjust it correctly. As you can see, the procedure is straightforward. Even a novice car enthusiast can handle it.

In conclusion, we note that the gaps need to be checked on new plugs (it is possible that the central electrode was bent during transportation). That’s all. We hope this article has helped you in resolving this issue.a.