Spark plugs for your car

Superior ignition with high-grade spark plugs

The spark plug is an important part in the ignition mechanism of a car as a connecting point between the ignition voltage and the combustion chamber. The spark plug triggers the actual explosion driving the car.

Construction of the ignition

The reliable ignition at the right moment of the air-fuel mix requires a powerful ignition spark which is generated by the spark plugs. A car dynamo generates a mere 12 – 24 V, which is way too low for an ignition spark. The voltage must therefore be amplified in order to enable ignition. The transformation takes place in the ignition coil, which is connected to the bodywork. This is a small box with two connecting cables and can be found on the engine side of the wheel arch. One of the cables comes from the generator, the other one connects with the distributor. At exactly the right moment, the distributor conducts the ignition current to the spark plug, which then ignites in its turn. Over the years, components have changed although the principal construction of an ignition system has remained the same. To prevent the ignition from overheating, the ignition current occurs as an impulse. Each time, the several tens of thousands of voltage are only maintained for an infinitesimal part of a second, thus guarding the system against fire damage.

Current under control

A spark plug must be able to safely conduct several tens of thousands of voltage which explains its special construction. A spark plug consists of a single electrode with a sturdy ceramic mantle, ending in a short screw tip connecting to the ignition's spark-plug terminal. Current always runs in a circuit and therefore the negative pole of the spark plug is always its outer thread in immediately contact with the inner thread of the cylinder head. It has a small brace right above the positive pole. The positive pole projects into the combustion chamber. If the voltage is transmitted to the spark plug, the desired spark ignites between the negative and positive pole igniting the air-fuel mix, causing the explosion pressing down the piston.

Simple construction and replacement

The specific advantage of a spark plug is its simple replacement in petrol-fueled vehicles. Everyone is (or should be) able to perform the essential maintenance of spark plug replacement. They are located in the cylinder head and screwed in and out with the fitting spanner. The following four steps must be observed:

1. Jamming spark plugs should be carefully unscrewed manually. Applying excess force could cause the thread to break, resulting in excessive damage which can only be repaired in a garage. 2. When the spark plug is removed, no particles should be allowed to penetrate in the combustion chamber through the plug opening. If necessary, plug it with a cloth. 3. When the spark plug is screwed in, be certain to insert it correctly in the screw thread, manually doing the first few turns before using tools. 4. Connecting the spark plug with the ignition requires following the correct ignition order. Always replace spark plugs one after the other and only disconnect the ignition cable when it is the turn of the next spark plug.

Checking when replacing

After its removal, the old spark plug should be inspected thoroughly. If it is greasy with oil or smudged by soot, this indicates a problem in the engine. Replacing by a new spark plug might be the solution. For the sake of safety it should be checked again after one or two hundred miles.

Quality and expertise when purchasing spark plugs

Spark plugs must match the engine. They can vary considerably in construction, length and heat value. Installing the wrong spark plug can quickly lead to engine damage. Basis for purchase of new spark plugs are the key numbers in the car's registration document. With a quality plug from NGK or Bosch you are on the safe side for the operational reliability of your car.