The letter A means that the thread of the screwed-in part is M14X. The number 17 is the heat rating, indicating that this spark plug is cold.
The letter D defines the length of the threaded part of the body. Information about the length of the threaded part, like all other data, is deliberately emphasized, since it is impossible to use longer or shorter spark plugs. In the first case, the threaded part will go deeper into the combustion chamber, will overheat and turn into a source of glow ignition with all the ensuing consequences.
If the spark plug has a short threaded part, the spark gap will be in a poorly ventilated area, due to which the spark plug will work unevenly. In addition, when it is time to screw a spark plug with a standard threaded part into the engine, unexpected difficulties will arise. The previously free part of the thread will be covered with a layer of carbon, which will be the culprit of the difficulties.
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The letter B indicates the design features, in this case the protrusion of the thermal cone.
Spark plugs are an important source of information. The condition of their threaded part and electrodes indicates the operating conditions of the spark plug.
A good spark plug that has already worked has some deposits on the insulator, so the insulator is light brown or grayish in color, the body is clean, there are no signs of wear on the electrodes. All this indicates that the conditions in which the spark plug operates fully meet its requirements.
Here is another spark plug. The body, the insulator and the electrodes are all covered in blackness. It is clear that the spark plug either works in very bad conditions or it got on the engine by accident, i.e. it does not match this engine. Some car enthusiasts install spark plugs from well-known companies (Champion, Marelli) on their cars without worrying about whether these spark plugs are suitable for the Zhiguli engine. In order not to get spark plugs blindly, use the recommendations of the Research Institute of Automotive Instruments. For VAZ vehicles equipped with A17DV spark plugs (GOST 2043-74*), it is permitted to install spark plugs of the following brands: FE55P ("Iskra", Poland), 14L-7Y ("Pal", Czechoslovakia), CLNY ("Lodge", Great Britain), FM14-175/2 ("Izolyator", GDR), N-11Y ("Champion", USA), W160T30 and W175T30 ("Bosch", FRG), BP-6ES (NJK, Japan).
Carbon deposits on spark plugs are not a random phenomenon. They are the result of such reasons as incorrect adjustment of the breaker-distributor contacts, violation of the gaps between the spark plug electrodes, a faulty capacitor, high-voltage wires, an over-enriched mixture, or prolonged engine idling.
On the third spark plug the electrodes are oiled. If the engine is no longer "in its first youth", then traces of oil on the spark plugs are a very definite sign - the piston group requires repair. Often another reason for the spark plug being oiled is damage to the cap 5 (see fig. 12) valves. The defect is accompanied by a noticeable oil consumption.
Burnt or heavily corroded electrodes, as well as a burnt, pitted insulator, indicate that the spark plug is not suitable (heat rating too low), incorrect setting of the ignition timing, use of low-octane gasoline. A spark plug damaged due to incorrect setting of the ignition timing (early) has distinct features: melted electrodes, damaged insulator.
In order for the spark plug to perform its functions well, all engine systems must work properly. In turn, the spark plug must also be in good condition, i.e. have no cracks or chips in the insulator, and the gaps between the electrodes must be within 0.5-0.6 mm. Usually, spark plugs work effectively for 30-35 thousand km, and then they are replaced with new ones. After every 10 thousand km, the spark plugs must be unscrewed, cleaned of carbon deposits, checked and, if necessary, the gap adjusted.
To perform this operation, you will need: a spark plug socket wrench, a spark plug feeler gauge, a stiff nylon brush, and a cleaning cloth (napkins, rags) and a special liquid for cleaning spark plugs. To prevent dirt from getting into the engine cylinders, freed from wires (take them off), Wipe the candles with a brush and napkins, and especially carefully the sockets where the candles are located.
You need to handle the spark plugs carefully, as a slight tilt of the socket wrench (and this is possible, because access, especially to the first candle, is not so free) — and the insulator is damaged. The removed spark plugs must be carefully examined, then thoroughly cleaned using a brush, a napkin soaked in a special liquid (if none — gasoline, alcohol) and wiped dry. The required gap is known, it remains to remind that all actions to adjust the gap can only be performed with the side electrode. The central electrode is inviolable: one careless movement — and the deformation of the insulator is guaranteed.
Install the treated spark plugs with sealing rings in place. First screw the spark plugs in by hand, then tighten them with a wrench, but without much force. When screwing in the spark plug, you need to "feel" the thread. The thing is that the spark plug body is steel, and the cylinder head is made of aluminum alloy. If you damage the thread of the socket, you will have to remove and repair the cylinder head.