Spark plugs are a valuable element to diagnose engine operation. Therefore, after dismantling the cylinder head, spark plugs must be examined carefully when the engine worked perfectly, ceramic insulator tip takes on a reddish-brown coloration, the electrodes were gray and dry spark plug is perfect. The presence of deposits carbon in the form of a fine layer of soot, show excessive use of the starter, playing little among the spark plug electrodes, advance very small, reduced pressure at the end of compression, spark plug too cold or mixture too rich (carburetor disturbed air damper defective air filter clogged, etc.).
When the insulator is white and very worn electrodes melt cause is too hot a spark plug, lean, very high ignition advance or gasoline with an octane rating lower. Spark plug has massive scabs soot can cause pre-ignition and production of soot deposits on the walls of the combustion chamber. The presence of oil on the spark plug is signal penetration of oil into the combustion chamber is attached segments, either through the intake valve stem and guide them; defect longer occurs when faulty crankcase ventilation causes increased pressure in this space or time to bath to put a quantity of oil too high.
If the insulator is cracked or broken without mechanical plug has been abused, the cause is either gasoline octane too small or too big advance, which caused uptime engine under severe knock. Apart from cases where there is damage or wear the electrode insulator, whose end no more than lower body plan in all other cases spark plugs can be reconditioned and reused if their life span does not exceed 15,000-18,000 kilometers 4-stroke engines and 7000-8000 kilometers 2-stroke ones.
Removing the spark plugs should be done only with special key because improvisations can lead to breakage of insulation, which otherwise may occur when the key is used carelessly. Before installation, clean carefully slot on the cylinder head (preventing dirt from entering the combustion chamber), grease thread spark plug with a little oil, check the existence and condition of seal ring, screw the initial spark plug by hand into place and then tighten socket wrench.
Tightening effort should be 4-5 times daN meter; too small an effort not guarantee seal, while one thread too high can damage the cylinder head, finally condemning this situation landmark expensive. It is also required that the seal assembly to have a single spark plug; its deficiency can compromise the seal and plug penetration depth too deep into the combustion chamber soot deposits intercedes thread (hampering subsequent dismantling), raises the thermal regime of this piece can even cause pre-ignition.
Mounting inadvertently two rings raises plug position by withdrawing it in the cylinder head; this will result in a slower spread of flame front and the possibility of spark caused by combustion, the cylinder head thread exposed to the flame. Not allowed under any circumstances the use of spark plugs of reductions or inadequate heat figure, leaky or defective insulation.