The distance between the electrodes is 0.7-0.8 mm on 1.6 liter engines and 1.1 mm on other engines. Spark plugs should be sandblasted at least every 10,000 km. After this, you should set the specified value for the distance between the electrodes. When installing, never push against the central electrode, as the porcelain insulator may crack. The best option for this is the combination of a dipstick and hook supplied by the spark plug manufacturer, which is used as shown in Figure 154. Before removing the spark plug, check for any foreign objects in the recess. A washer, bolt, stone or the like falling into the spark plug hole can destroy valves, valve seats or the cylinder head when the engine is first started. By the appearance of the spark plug, we can draw conclusions about its suitability and operation, carburetor adjustment, mixture composition and engine condition. General criteria:
Pic. 154. Control of the distance between electrodes (left) and setting the distance between the electrodes (on right)
- Candles are normal
The insulator leg is covered with a weak, gray-yellow to brown coating. On the electrodes, except for burnt areas, there is a gray-yellow to brown coating. The interior of the housing is light brown or yellowish to black-brown. The engine is in good condition. The number of candles is chosen correctly
- Candles are covered with soot
The insulator leg, electrodes and the inside of the housing are covered with a thick powdery black-gray greasy coating. The reason for this is too rich a mixture, insufficient air, turning on the air damper for too long, too high a distance between the electrodes, or choosing a spark plug with too high a heat rating, which remains cold during operation. Install spark plugs with a different heat rating.
- The candles are oily
The insulator leg, electrodes and body are covered with a greasy, shiny layer of soot. The cause may be the penetration of engine oil into the combustion chambers or wear of the cylinders and pistons.
- Overheating of spark plugs
The insulator stalk is covered with a dark brown to grey-black, glassy, caked deposit, often with a thickening layer of plaque at the base of the stalk. The electrodes, especially the central electrode, are affected. The outer surface is often rough, swollen and corroded. The cause may be a too lean mixture, a disconnected spark plug, poorly closing valves, or the use of spark plugs with a low heat rating, which causes them to overheat. When refueling with lead-containing fuel, the insulator leg is gray in normal condition. Deposits between the porcelain insulator and the central electrode are removed by sandblasting. Before screwing in the spark plug, make sure the threads are clean. Since the service life of spark plugs is usually 15,000 km, it is enough to perform one cleaning after 10,000 km. When screwing in the spark plug, do not overtighten it, as the sealing washer may be damaged. Do not exceed a tightening torque of 20-30 Nm. An extended spark plug wrench is required to access the spark plugs.