Efficiency of Internal Combustion Engine ignited by sparking, as one of the most refined existing sources of mechanical energy, i.e. its capability to work at all, is in direct relation with ignition quality of one small component that has no any mobile elements, of spark plug. Spark plug can be defined very simply as a device that brings high voltage to the combustion chamber and transforms it into spark, making possible ignition of fuel and air mixture. Although the spark plug looks simply and can be defined easily, its development and improvement has been lasting over 100 years, parallel with development of engines ignited by sparking. Like an engine and a modern spark plug is carefully made product based on special technologies from ceramics technique, metallurgy and precious machining. Spark plug as one of the basic particularity of spark ignition engine, has duty to put in ignition energy into combustion chamber, and to enable combustion of fuel and air mixture by spark formed between its electrodes. In order to perform that primary duty, to give a high voltage spark at appropriate spot into combustion chamber, to enable a reliable engine start, to guarantee engine smooth running, to be durable for the long work period at maximum engine power, a spark plug has to respond to the next requirements:

Electrical requirements
At spark plug operation with electronic ignition devices it may appeared voltages over 30.000 V, whereas the residues of combustion such as soot, carbon, and ashes separated from fuel and oil additives, have electrical conductivity only at certain thermic conditions. However, under those circumstances, even at high voltages, it is not permitted appearance of short circuit between electrodes. Electrical insulator resistance has to be enough high, also by the temperature of 1.000 °C and mustn't be changeable during spark plug operation.

Mechanical requirements
With regard to the position of a spark plug, placed into combustion chamber of fuel and air mixture, it has to oppose the pressures (by 50 bars), which exist periodically in combustion chamber, without loss of gas tightness. Additionally, it is also requested a high mechanical strength, especially ceramics and metal spark plug shell for connection with engine cylinder head.

Chemical requirements
On the occasion of the incomplete combustion in an engine cylinder, integral fuel elements are deposited ad the aggressive residues on spark plug insulator nose. High temperatures in combustion chamber affect this spark plug part so it warm up by becoming red-hot. In such condition this insulator nose is exposed to the chemical processes that are going at high temperatures. Those aggressive residues, deposited on insulator nose and electrodes, can considerably change characteristics of spark plug.

Thermic requirements
During operation spark plugs takes on the heat from the hot gas combustion products and just after that is exposed to cold mixture of air and fuel. Therefore spark plug insulator nose must satisfy high requirements for thermo-shock resistance. For the functional operation request, spark plug also must take away the heat, took on from combustion chamber, to engine cylinder head while connecting side of spark plug should warm up just a little. Consequently, the end of spark plug can be cold like ice, but ignition tip, far away only about seventy millimeters, is exposed to temperature over 850 °C.

Spark plug structure
Spark plug consists of metal, ceramics and glass, i.e. from materials of different characteristic. Each of those components makes a strong influence to the function and reliability of spark plug operation. This is provided by special design and specific characteristics of installed materials.

SPARK PLUG SELECTION

Spark plug, particularly the nose of a spark plug, is subjected to extremely high thermodynamic loads in an environment where oil, lead and carbon foulings are present. In order that a spark plug might properly perform its function in an engine it must be designed so that its nose always remains within correct heat ragne, regardless motoring conditions, thus securing correct self-cleaning (burning off the fouling depositss) but not causing self-ignition (sparkless ignition). In order to satisfy the above conditions, our designers cooperate with engine designers and accomodate the spark plug construction to suit the engine requirements, particularly regarding the thermal loads, which ultimately results that each engine type has its "own" spark plug, regarding the heat value and other design parameters, from the extensive choice of ENKER® spark plugs.
Consequently, when selecting or replacing spark plugs it is most important to pay attention to the heat value, thread diameter and length and seat type (see "Symbol Explanation"). If your engine is factory fitted with ENKER® spark plugs, you cannot go wrong if you as your dealer for the identical spark plugs. But if your engine is titted with spark plugs of another manufacturer, the proper thing to do is to select your spark plugs in our Catalog. If our Catalog does not list your engine type.model, we kindly refer you to the Comparison Chart within this Catalog which gives you a table of ENKER® spark plugs and their equivalents manufactured by world renowned manufacturers.

Presuming that you made correct selection of the spark plugs through the use of our instructions titled "Spark Plug Selection"; you should also PAY ATTENTION to the gap setting between the electrodes as recommended by the engine manufacture in his technical manual (maintenance schedule or technical data list); you can also use our Catalog. These data should be compared with the factory set spark plug gap and corrections should be made if necessary. Make quite sure before you fit plugs that the spark plug seat in the cylinder head is perfectly clean. Screw the spark plug into its seat by hand until the washer or its seat contacts the cylinder head. As to avoid damage in the cylinder head we recommend that you use a torque spanner set to the tightening figures given in our table "Tightening Torque".
If you tighten spark plugs by spark.plug spanner, then new spark plugs with flat seat (gasket type) should be tightened approx. 90°. Those with conical seat are tightened approx. 15°, the same applies to used spark plugs with a flat seat and deformed gasket. You should be very careful when tightening spark plugs with conical seat (without gasket) because of seat vulnerability in the cylinder head.

The gap between the central and earth electrodes is an important factor for correct engine running as regards both, the loading, and the economy of the engine. Incorrect setting of the gap can result in misfiring, engine power loss, fouling of the electrodes, etc. Because of the electro-chemical erosion, which is a normal development during the operation, the spark plug gap should therefore be periodically checked and reset, if necessary, by bending the earth electrode only. Such adjustments are limited by the basic geometry of the electrodes, so it is suggested that the spark plugs be replaced by new ones after 12.000 to 15.000 kms in case of fourstroke engines, or after 6.000 to 8.000 kms with two-stroke engines if full performance of the engine is to be maintained.