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Technical Bulletin

Trouble Shooting Information About
NGK Spark Plug

 

Beware of using Fake Spark Plug

 The use of imitation spark plugs can damage your engine

Reports from defrauded consumers clearly show that using imitation spark plugs can damage your engine.

       

Why use potertially harmful imitation spark plugs in the engines of valuable cars, motorcycles, and general-purpose machinery?

To avoid this kind α problem, always insist on genuine NGK brand spark plugs.

 

Even spark plugs with unique brand name can be imitation counterfeit if the part numbers resemble those of another brand.

The flagrant use of imitaton brand spark plugs could result in either criminal or civil prosecution, confiscation of inventory, or other means of punishment.

     

 

How to identity imitation Spark Plugs

 

 View Explanatory Video here.

 

Troubleshooting

1. Collapse of the Spark Gap

	1) A protective cap is used to prevent collapse of the gap, but collapse may still occur depending on the height that the spark plug is dropped from and where it is dropped. See Photo 1.	Photo 1: Collapsed gap
	2) When a claim is made about collapse of a gap, check for the dents that should remain on the protective cap and box. 3) The cause of the collapse of a spark gap is dropping of the spark plug and it does not indicate a production problem. No damage to the protective cap or product box is caused in the production processes.	Photo 2: Collapsed protective cap	Photo 3: Dent left by the outer electrode (box for one spark plug)

 

2. Spark Leak

	1) Occasionally, plugs with rust-colored burn marks on the surface of the insulator around the firing end are seen. Among the additives included in gasoline (for example the value-improving agent octane) there may be components like manganese. If compounds of manganese and other substances generated by combustion accumulate on the insulator around the firing end, the surface may become a rusty color. When heated, this coating may reduce the insulating performance and cause misfires.	Photo 1: Adhesion of products of oxidation of additives
	2) When fitting spark plugs, some people apply an anti-seizure agent like molybdenum to the screw thread. (Never use such an agent: it can lead to the application of excessive torque and overtightening.) This anti-seizure agent may adhere to the insulator and, when heated, will also degrade insulation resistance and may cause misfiring.	Photo 2: Adhesion of anti-seizure agent and other substances

 

3. Dry Fouling and Wet Fouling of the Plug

	1) Carbon fouling If the air and gasoline mixture is rich (i.e., it contains a higher proportion of gasoline), carbon will be produced by incomplete combustion. If this carbon accumulates on the firing end of the plug, the insulator resistance between the center electrode and the metal shell will be reduced and this may cause misfiring. See Photo 1. In cold regions (or in winter), because the external air temperature is low, the gasoline does not form a fine mist and therefore does not mix well with the air. Entry of gasoline in liquid form into the combustion chamber leads to incomplete combustion and makes it easier for carbon to form. There is hardly any carbon generation in vehicles that use a gas fuel, LPG or CNG, like taxis for example. Wet fouling is seen, for example, in motorcycles (with two-stroke engines). With oil and gasoline covering the carbon that has adhered to the firing end, the insulation resistance value drops abruptly, causing misfires. See Photo 2.	Photo 1: Dry fouling	Photo 2: Wet fouling
		Schematic drawing
	2) The causes of carbon fouling are: 1) Causes relating to the fuel system Carburettor maintenance fault Injector fault Oxygen sensor fault (sensor fault) Clogging of the air cleaner element, etc. 2) Causes relating to the ignition system Delay in the ignition timing Plug heat range is too high
	3) Insulation resistance A high voltage is applied to the center electrode but if there is carbon adhering to the firing end of the plug the insulation resistance is lowered and spark leakage occurs, so this voltage does not result in a spark across the spark gap. Normally, when there is no adhering carbon, the insulation resistance is an infinite value but when there is adhering carbon and the insulation resistance reaches around 10 MΩ or less spark leakage occurs and no spark can be produced across the spark gap. Naturally this means the engine will not start.	Photo 3: Insulation resistance tester
	4) The cause of carbon fouling lies in the fuel system. It is not a problem with the plug. If the carbon adhering to the plug is cleaned off (by sandblasting), the function of the plug will be recovered and it will be possible to re-use it. However, few motor maintenance or repair facilities have such a plug cleaner installed, so our recommendation is to change the plug if possible. Note: If dry fouling occurs at only one of the cylinders there is the possibility that the problem is caused by the plug. (For example, while fitting a plug the wrench can slip and damage the core of the insulation although this is not detectable from the external appearance, and spark leakage may occur as the result of this damage.)

 

 4. Problems with the Firing End

	1) Breaking of the insulation Type 1 (See Photo 1) When selecting a plug, make sure that the standard plug will not go outside the optimum temperature range while engine combustion is normal (refer to the "Plug Temperature and its Effects" chart below). If for any reason (water leakage, oil leakage, etc.) the engine starts knocking or detonation occurs, the temperature of the combustion gas will rise sharply and the plug, piston and valves will overheat. Overheating of the plug causes the center electrode to expand, and this can break the insulation.	Photo 1: Breaking of the insulation
	2) Breaking of the insulation Type 2 (See Photo 2) This is the situation where deposits (products of combustion of oil, etc.) penetrate into the gap between the center electrode and insulation at the firing end, expanding the center electrode and causing the insulation to break. Normally, deposits do not penetrate into this gap. If the engine overheats, the engine's cylinder head may distort. This means that cooling of the combustion chamber will fail which in turn means that knocking will occur more easily. Repeated knocking leads to abnormal pressure and vibration in the combustion chamber. This abnormal pressure and vibration causes the deposits that have accumulated in the combustion chamber to scatter as fine particles and enter gaps in the plug.	Photo 2: Entry of deposits
	3) Melting of electrodes (See Photos 3,4 and 5) If the firing end overheats far beyond the optimum temperature range, the fuel-air mixture may ignite and combust in advance of the normal ignition timing (this is called "pre-ignition").

Photo 3: Electrode overheating	Photo 4: Electrode melting	Photo 5: Holed piston

Excessive advance of ignition timing → Fuel-air mixture too lean → Leakage of cooling water or oil → Plug incorrectly tightened → Plug with a low heat rating used → Plug heat rating reduced by accumulation of deposits →	Adjust the ignition timing. Inspect and adjust the fuel system. Inspect and repair the leak. Tighten plugs with the recommended torque. Use a plug with the standard heat rating. Change the plug.

If the engine is not performing properly and on removing a spark plug it is found that the electrodes have melted or the porcelain insulation has broken, this could be construed as a spark plug fault, but note that some other possible causes for the poor engine performance are problems with the valves, valve seats or pistons.

 

  5. Broken Thread

The tightening torque for spark plugs varies depending on the thread diameter of the plug. If a plug is tightened with a torque exceeding the recommended torque, the thread could break. See Photo 1.		Photo 1:
	1) Apart from overtightening, another possible cause of a thread break in a plug is the application of an anti-seizure agent or oil when fitting the plug, since this lowers the friction resistance and means that the thread can be turned more than necessary. Never use an anti-seizure agent or oil.
	2) When fitting a spark plug, use a torque wrench and tighten it with the recommended torque. For situations where it is not possible to use the list of recommended torques and a torque wrench, the turning angles to achieve correct tightening are also given below.

Plug thread diameter	Tightening torque
18mm	35 - 40N · m(3.5 - 4.0kgm)
14mm	25 - 30N · m(2.5 - 3.0kgm)
12mm	15 - 20N · m(1.5 - 2.0kgm)
10mm	10 - 12N · m(1.0 - 1.2kgm)
8mm	8 - 10N · m(0.8 - 1.0kgm)

	Tightening torque
Taper seat type (plug with no gasket)	10 - 20N · m(1.0 - 2.0kgf-m)

 Turning angles for tightening
Plugs with thread diameters of 18 and 14 mm · · · Half to two-thirds of a turn (180° to 240°)
Plugs with thread diameters of 12 and 10 mm · · · Half a turn (180°)
Plugs with thread diameters of 8 mm · · · · · · · · · · One third of a turn (120°)

 

 6. Breakage of the Insulator 

If, because of the construction of the engine, the position of the spark plugs makes it difficult to fit or remove them (or even to see them), the plug wrench may tilt off-axis or slip. If the wrench slips and its inside wall strikes the ribbing on the plug's insulator, or its terminal, the insulator may break.		Photo 1
1)	If the plug wrench slips and its inside wall strikes the insulator ribbing (see "1." in the illustration), the insulator may be broken as shown in Photo 2. The location of the break may not be visible (inside the metal shell) as shown in Photo 3.
2)	Alternatively, if the inside wall of the plug wrench strikes the terminal (see "2." in the illustration) the insulator may crack from the tip as shown in Photo 4.
Note: Since this kind of problem is most likely to occur with engines where fitting and removing spark plugs is difficult (where plug changes are accomplished by feeling by hand), you can prevent trouble by using a sturdy wrench and performing the operation carefully in such cases.

Photo 2

Photo 3

Photo 4 (terminal)

 

  7. Tear in the Metal Shell Beneath the Hexagonal Portion 

The return torque required to remove a spark plug is sometimes abnormally high. Forcibly removing the plug in these circumstances can cause tearing of the metal shell beneath the hexagonal portion. See Photo 1.		Photo 1
1)	The reason for an abnormally high return torque is that the spark plug was fitted with excessive torque. This may also cause seizure of the plug thread and thread in the engine head
2)	If the spark plug cannot be removed because the torque required is too great, it is sometimes effective to warm up the engine and then spray the plug thread section liberally with a penetrant, then wait a short while before attempting removal again.

 

  8. Breakage of the Center Electrode Tip

Spark plugs with fine electrodes made of iridium or platinum have "Do not adjust the spark gap" written on their packing boxes.		Photo 1: Center electrode tip breakage
1)	This is to prevent the general user adjusting the spark gap and breaking or removing part of the fine center electrode tip as the spacing tool makes contact with it. See Photo 1.
2)	When the tip of the center electrode is broken, a nick is sometimes left on the ground electrode too.

 

  9. Insulator Spark Leakage (Flashover)

Flashover is the phenomenon where sparks are discharged between the terminal and metal shell of the spark plug. It occurs when the voltage across the plug itself is 25,000 V to 30,000 V.		Photo 1: Center electrode tip breakage
1)	If the spark gap has widened as a result of terminal wear, or if the compression pressure is high as in a turbo engine, a higher voltage is required between the electrodes and flashover becomes more likely to occur. In practice, flashover does not normally occur because the flashover voltage is blocked by fitting a plug cap that makes a good seal with the insulator.
2)	However, if the seal part of the plug cap deteriorates (it hardens over time), or if water droplets get inside the plug cap, flashover becomes more likely, so periodic maintenance of the plug caps is necessary.
	Reference: Flashover leaves black streaks on the insulator. These streaks are formed as the rubber of the cap seal is melted by a spark discharge and then deposited on the insulator. See Photo 1.

 

  10. Breakage of the Plug's Ground Electrode

Each engine generates its own individual vibrations. The higher the engine's revving range and output, the stronger is the vibration. Since the spark plugs are fitted in the engine's cylinder head, they are subject to the same vibrations as the engine. As shown in Figure 1, the tip of the ground electrode vibrates with the weld as the fulcrum. If the ground electrode's weld becomes unable to withstand the vibration fatigue, it will break. See Photo 1. Note also that if the spark plug is insufficiently tightened when fitted (i.e., the torque was less than the standard tightening torque), the plug may loosen. If it does loosen, it will be subject to abnormal vibration and this can cause the ground electrode to break off. Note 1: The standard spark plug types fitted in high-revving, high-output engines are the multi-electrode type that is not so susceptible to electrode breakage and the type with a sparking portion that does not project very far; be sure to use the authorized spark plugs.

Fig. 1: Diagram of Ground Electrode Breakage Photo 1: Broken ground electrode