Thread: ~ All About Spark Plugs ~
07-10-2006, 12:14 PM #1
~ All About Spark Plugs ~
How a Spark Plug Works:
The basics of a spark plug is that it must perform two primary functions.
1. To Ignite the Air/Fuel mixture
2. To REMOVE the heat out of the combustion chamber
Spark plugs transmit electrical energy that turns fuel into working energy. A sufficient amount of voltage must be supplied by the ignition system to cause the spark to jump the across the spark plug gap, thus creating what is called Electrical Performance.
Additionally, the temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called Thermal Performance and is determined by the heat range of the spark plug.
It is important to understand that spark plugs CANNOT create heat, only remove it! The spark plug works as a heat exchanger, pulling unwanted thermal energy away from the combustion chamber and transferring the heat to the engine's cooling system. The heat range is defined as a plug's ability to dissipate heat. The rate of heat is determined by:
• The insulator nose length
• Gas volume around the insulator nose
• Materials and/or construction of the center electrode and porcelain insulator
Now to the actual function: As the Ignition is triggered it sends the spark through the rotor, to the cap, down the wire and then it jumps the gap of the spark plug, a spark kernel is created that ignites the air/fuel mixture in the combustion chamber. Proper timing of this spark is not the only concern as described above. You must have the proper heat range (described later) as well as the correct gap.
Opening The Plug Gap:
On weaker or stock ignitions, opening up the gap CAN increase the spark kernel size, thereby creating a more efficient burn. The problem lies in that any added gap creates more strain on the other ignition parts.
• Coils may not have enough stored energy to fire, or in the least case, not enough energy to cross the gap, creating a miss-fire.
• Plug wires will break down due to the added resistance as the spark tries to reach ground.
Removing the Old Spark Plugs
1. Find the spark plugs, located in a row along one side of the engine and attached to thick wires, called spark plug wires.
2. Change one spark plug at a time, always putting the plug wire back on before changing the next spark plug (see warning below).
3. Pull off one spark plug wire where it attaches to the plug. There is a little rubber boot at the plug end of the wire; pull on this part. Pulling higher up on the wire can damage the spark plug wire and cause it to separate.
4. Blow or wipe away any dirt or debris around the spark plug. You do not want anything to fall into the cylinder while the spark plug is out.
5. With the spark plug socket and a ratchet, remove the spark plug by turning it in a counterclockwise direction. You may need an extension for your ratchet if the spark plugs are deep-set or not directly accessible. Ratchets with flexible heads are especially helpful for hard-to-reach spark plugs. (Image 3)
6. Check the spark plug to make sure it needs replacing. A good spark plug should be lightly coated with greyish brown deposits. If heavy deposits are present, if the spark plug is black or if the electrode or core nose are damaged, the plug needs to be replaced.
Your socket set should have a "spark plug socket" (usually with a little padding/grip inside it) just for spark plugs.
Make sure the car is off and let the engine cool before changing the spark plugs.
Change one spark plug at a time, putting the wire back on after you're done. In an automobile, If you pull all the wires off at once, you may put them back on the wrong spark plugs; this changes the firing order, and your car will run badly or not at all. If you must take all the wires off at once, label them with white correction fluid or with masking tape and a marker. For Personal watercraft, this is not crucial as there are only 2-3 and the plug wires are cut to length and easy to identify.
Gapping the New Spark Plugs
Spark Plug Gap
1. Find the chart listing the proper "gap" for your application in the service manaul.
2. Insert the spark plug gapping tool in the gap between the metal center electrode and the metal side electrode of the plug's tip.
3. Look at the tool's ruled edge and find the gap's measurement. If it is too big, bend the spark plug's end with the tool to widen the gap. To make the gap smaller, push the side electrode (the metal part at the very top) against a hard service.
4. After adjusting, measure again. Repeat this procedure until the gap matches the specification listed in your car's manual.
5. Repeat with each plug.
Spark plug gap specifications are listed in inches and/or millimeters. The gapper will have inches on one side and millimeters on the other.
Make sure you buy the right spark plugs for your application, model, make and year.
Installing the New Spark Plugs
1. Hand-tighten each spark plug in place. If you feel any resistance, stop and start over to prevent cross-threading.
2. Tighten the plugs with a socket wrench until snug. Do not overtighten.
3. Replace the spark plug wires. Usually, you will hear a soft pop when the plug wire snaps onto the plug.
4. Start the engine. Listen. If the engine runs roughly or doesn't start, make sure the wires are pushed all the way onto the new plugs.
Improperly gapped plugs will make your car run roughly, start poorly and have bad gas mileage.
Always Clean the threads
Clean the threads when you remove the plugs, and before installing the new ones. You will clean out a lot of crummy carbon deposits off the threads which could otherwise go back into the cylinder and pollute your new oil.
Change spark plugs with your oil service, and always change the oil filter at the same time. If you're going to get under the car, make it worthwhile!
Always, always, make sure your plugs and leads are firmly back in place, don't overtighten plugs or the oil drain plug like a gorilla.
Below is a list of external influences on a spark plug's operating temperature.
• The following symptoms or conditions may have an effect on the actual temperature of the spark plug. The spark plug cannot create these conditions, but it must be able to cope with the levels of heat...if not, the performance will suffer and engine damage can occur.
Air/Fuel Mixtures seriously affect engine performance and spark plug operating temperatures.
• Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor driveability
• Lean air/fuel mixtures cause plug tip and cylinder temperature to increase, resulting in pre-ignition, detonation, and possibly serious spark plug and engine damage
• It is important to read spark plugs many times during the tuning process to achieve the optimum air/ fuel mixture
Higher Compression Ratios/Forced Induction will elevate spark plug tip and in-cylinder temperatures
• Compression can be increased by performing any one of the following modifications:
a) reducing combustion chamber volume (i.e.: domed pistons, smaller chamber heads, mill ing heads, etc.)
b) adding forced induction (Nitrous, Turbocharging or Supercharging)
c) camshaft change
• As compression increases, a colder heat range plug, higher fuel octane, and careful attention to ignition timing and air/fuel ratios are necessary. Failure to select a colder spark plug can lead to spark plug/engine damage
Advancing Ignition Timing
• Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-100° C
Engine Speed and Load
• Increases in firing-end temperature are proportional to engine speed and load. When traveling at a consistent high rate of speed, or carrying/pushing very heavy loads, a colder heat range spark plug should be installed
Ambient Air Temperature
• As air temperature falls, air density/air volume becomes greater, resulting in leaner air/fuel mixtures.
• This creates higher cylinder pressures/temperatures and causes an increase in the spark plug's tip temperature. So, fuel delivery should be increased.
• As temperature increases, air density decreases, as does intake volume, fuel delivery should be decreased
• As humidity increases, air intake volume decreases
• Result is lower combustion pressures and temperatures, causing a decrease in the spark plug's temperature and a reduction in available power.
• Air/fuel mixture should be leaner, depending upon ambient temperature.
• Also affects the spark plug's tip temperature
• The higher the altitude, the lower cylinder pressure becomes. As the cylinder temperature decreases, so does the plugs tip temperature
• Many mechanics attempt to "chase" tuning by changing spark plug heat ranges
• The real answer is to adjust air/fuel mixtures by rejetting in an effort to put more air back into the engine
Here is a good article on HOW TO READ SPARK PLUGS
For two Stroke engines, Eric Gorr has this good link below on reading two-stroke plugs.
Here is a plug symbol chart for NGK plugs
As well as reducing electrical noise for radio, television and mobile telephones etc, many modern ignition systems require resistor plugs to stop electrical noise from interfering with the vehicle's on-board electronic control units (ECUs). If non-resistor plugs are used in place of resistor ones, the result can be malfunction and in some cases immobilisation of the vehicle. Resistor spark plugs should always be fitted, therefore, where specified. NGK resistor spark plugs contain a single ceramic monolythic resistor of approximately 5000 ohms.
Because of the type and construction of the resistor (ie no springs), the problems of vibration and sudden changes in temperature that can occur with some other brands do not apply. The function of the resistor is to reduce electrical noise generated by the ignition system. The most effective place to situate a resistor in the high tension circuit is as close to the spark plug as possible. This makes the spark plug an ideal place to house the resistor. Because the resistance value is only approximately 5000 ohms, there is no detrimental effect on engine performance, power output, vehicle emissions etc. It is also a fact that many motor sport world champions only use NGK resistor spark plugs. In nearly all cases - apart from some very old low output ignition systems - resistor spark plugs can be used in place of the non resistor versions. www.ngk.com
07-10-2006, 12:19 PM #2
J gapping and indexing plugs
Index the plugs so they fire towards the exhaust, and J gapping will help the spark burn unobstructed.
Last edited by XL1200Ltd-Keith; 01-01-2010 at 08:11 PM.
07-10-2006, 12:58 PM #3
Here is some good information over Indexing Spark Plugs
Indexing refers to an old racer's trick whereby the spark plugs are installed so that the ground electrode is oriented to face the intake valve (usually) in an effort to "open up" the spark to the incoming air/fuel charge.
This is accomplished by placing a washer underneath the spark plug's shoulder area (of a specified thickness) so that after properly torqueing the spark plug, the electrode would be pointed in the desired direction, usually towards the incoming air/fuel charge from the intake valve.
Some racers have discovered that certain engine configurations made more power with the spark plug pointed away from the air fuel mixture.
It is important to note that any power increase will be small, typically 1-2% of total engine output, and the proper indexing orientation can only be discovered after extensive engine dyno testing.
07-10-2006, 05:44 PM #4
07-10-2006, 05:45 PM #5
07-10-2006, 06:27 PM #6
07-10-2006, 07:46 PM #7
Ok some one help the Dumby (me). I thought with a two stroke you index to the exhaust side.and a four stroke towards the intake?
07-10-2006, 08:52 PM #8Originally Posted by RX951
Currently in the Nextel Cup Racing series, they use a spark plug that is known as an Angled “A” Gap. This design offers an angled ground electrode that is shorter than the “J” and provides additional exposed gap thus a greater bang for the buck when dealing with the high powered engines of today. In (NASCAR) , A-Gap plugs are popular.
07-19-2006, 05:52 PM #9
01-15-2007, 12:39 PM #10
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