6/23/2014
Spar k Pl ug Help
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Spark Plug Help
How a spark plug works A spark plug basically consists of 5 components:
an ex remey remey g me me ng po n characteristics characteristics of iridium. iridium. The intense spark from the Iridium IX spark plug improves the throttle response, acceleration and fuel efficiency of your motorcycle. Trivalent metal plating on these sp ark plugs will make sure they don't corrode or cause seizing. Sold individually.
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The terminal allows allows electrical connection from the plug w ire to the spark plug The c eramic eramic insulator insulator isolates isolates the terminal terminal and center electrode ends from the ground electrode and hous es the resistive element element of the plug The body of the spark plug consists of the threads for installing the plug as well as a hex for turning the plug with a wrench The center electrode provides the source point of the spark The ground electrode provides the destination destination point for the s park The operation of a spark plug occurs as follows: The engine ignition ignition control circuit determines determines w hen the spark is to oc cur. At this this time, a very high voltage pulse is delivered to the spark plug terminal end. The voltage is so high that electrical current can flow across the gap between the center electrode and the ground electrode, resulting in a spark. Of course, it is this spark which ignites the fuel-air fuel-air mixture that has been drawn into and c ompressed in the engine combustion chamber. However simple a spark plug may be, the construction of one is critical. A spark plug must be able to withstand frequent high voltage pulses, high pressures , high temperatures, vibration vibration and combus tion by-products. Each of these variables variables c ontribute to the possible failure failure of a spark plug.
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Spark plug failure A spark plug can phys ically ically be damaged. For example, the electrode c an by melted or burned, or the ceramic insulator can break. Stripped threads can also occ ur, but this is likely likely caused by improper installatio installation. n. T ypically, ypically, though, a spark plug will will fail fail by what is referred to as fouling. fouling. Spark plug fouling fouling occ urs w hen the insulator insulator nose at the c enter electrode accumulates either fuel, oil or carbon. T his accumulation allows the high voltage to travel along the insulator nose to ground rather than jumping the electrode electrode gap. A fouled fouled spark plug can sometimes be cleaned to restore normal operation. Often, how ever, replacement is the only solution. Causes of Fouling: Fouling: Continuous low speed engine operation Spark plug "heat range" too cold (the selected spark plug is incorrect and cannot reach the correct operating temperature) Air-fuel mixture too rich resulting in accumulation of fuel deposits around the insulator insulator nose and electrode Reduced compression and oil usage due to worn piston rings, worn cylinder or w orn valve guides guides
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Spark Plug Help Excessive premix oil in fuel for two stroke engines Retarded ignition timing Ignition system not delivering the correct voltage Spark plug gapped incorrec tly Dirt, moisture or other c onductive contamination in and around the spark plug terminal connection Failed spark plug wire Dirt, moisture or other c onductive contamination in and around the magneto/alternator Loose, broken or c ontaminated ignition system wiring connections A spark plug can fail by overheating, which can cause the electrodes to wear quickly, melt or break apart. The failure mode of the electrode depends in part on the type of electrode material. Engine overheating has an array of causes and harmful effects not limited to a spark plug. Causes of Overheating: Incorrect spark plug heat range (the selected spark plug is the wrong type and cannot dissipate the correct amount of heat) Spark plug not tightened to the correct torque or the gasket is missing advanced ignition timing Fuel octane rating too low or excessive engine compression due to excessive combustion chamber deposits (engine will knock) Air-fuel mixture too lean Continuous engine operation under excessive loads Insufficient engine cooling or lubrication
How to visually check spark plugs The following images show the visual condition of a spark plug given each specific problem listed.
Normal spark plug
Dry Fouled spark plug
Wet Fouled spark plug
s par k plu g Wit h Dep os it s
s pa rk plug Ov er heat in g
Ele ct ro de Ox id at io n
Electrode Erosion
spark plug Overheating
Electrode Melting
Insulator Breakage
Visual inspection images courtesy of NGK. .
How to check a spark plug with an ohm meter If a spark plug looks normal, but you still suspect it is the problem, you can check it with an ohm meter in two ways:
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Spark Plug Help Connect one test lead to the spark plug terminal and the other lead to the center electrode (note: you may need to clean the center electrode to have good continuity with the meter lead). If you have a resistor type spark plug, you should have a reading of s everal thousand ohms (around 5k ohms, plus or minus 1k ohm or so). If you have a non-resistor type spark plug, the meter should display very low ohms or zero. If this measurement shows an open circuit condition, the plug should be replaced. If the measurement indicates a good spark plug, proceed to the next test.
Leave the test lead on the spark plug terminal end and move the other lead the ground electrode or any place on the metallic body, below the ceramic insulator. It is important that you keep at least one hand from touching the plug or test lead tip to avoid a false reading. T his measurement should show an open circuit measurement. Any measured resistance (even in the meg ohm range) is bad and will cause the high voltage pulse to bypass the high resistance air gap, resulting in no spark or weak spark.
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