Bougies d'Allumage

Guide pour Bougie d'Allumage

Le transfert de taux de chaleur est déterminé par:
* La longeur de l'embout de l'isolateur
* Le Volume du gaz autour de l'embout de l'isolateur
* Les matériaux/ la construction de l'électrode centrale et l'isolateur en porcelaine
La gamme de chaleur d'une bougie d'allumage n'a pas de relation avec l'actuel voltage transferré à travers la bougie d'allumage. Plutôt, la gamme de chaleur est une mesure de la capacité de la bougie d'allumage à retirer la chaleur de la chambre de combustion. La mesure de la gamme de chaleur est déterminée par plusieurs facteurs; la longeur de l'embout de l'isolateur central en céramique et sa capacité à absorber et transférer la chaleur de combustion, la composition du matériau de l'isolateur et le matériau de l'électrode centrale.

La longeur de l'embout de l'isolateur est la distance a partir de firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C.

DPR9EA-9

Field one: Thread Diameter and Wrench Size

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HOT TYPE (BP 5 ES)
It has a larger surface exposed to the combustion gasses, it dissapates heat slowly, its firring end heats up quickly

COLD TYPE (BP 7 ES)
It has a smaller surface exposed to the combustion gasses, it dissipates heat quickly, its firing end does not heat up quickly

Spark Plug Problems

Keep in mind the insulator nose length is a determining factor in the heat range of a spark plug, the longer the insulator nose, the less heat is absorbed, and the further the heat must travel into the cylinder head water jackets. This means the plug has a higher internal temperature, and is said to be a hot plug. A hot spark plug maintains a higher internal operating temperature to burn off oil and carbon deposits, and has no relationship to spark quality or intensity.

Conversely, a cold spark plug has a shorter insulator nose and absorbs more combustion chamber heat. This heat travels a shorter distance, and allows the plug to operate at a lower internal temperature. A colder heat range is necessary when the engine is modified for performance, subjected to heavy loads, or is run at a high rpm for a significant period of time. Colder spark plugs remove heat quicker, reducing the chance of pre-ignition/detonation. Failure to use a cooler heat range in a modified application can lead to spark plug failure and severe engine damage.

Put the plug-wire end of the new plug in the socket and, holding just the extension, push it all the way in. Now carefully guide the spark plug into the hole. Try not to ram it in or bang it on anything because this can alter the gap or even worse damage the thread on the plug. With it sitting in the hole, begin to screw the new plug in by hand slowly. Starting them off by hand instead of using the wrench will keep you from accidentally cross-threading one of the plugs. Screw it in by hand until it stops, then put the wrench on the end and tighten it snugly. If you have a torque wrench, you can torque it to spec, but if you don't, just make it tight without overdoing it. The metal in there is soft and can be damaged by over tightening. If you are pulling hard enough to make a sound come out of your mouth, like a grunt, you're overdoing it
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If things go wrong.
Spark Plug Engine Head Threadsaver ( 12mm and 14mm)

The ThreadSaver is a collapsible tap with a centre rod that enables the user to regulate the amount of pressure at the thread cutting end of the tool. It enables the user to adjust the cutting depth of the thread by simply pushing the rod toward the cutting head to increase depth or retracting the rod to reduce cutting depth.
To start the operation, the expanding rod is removed. This allows the collapsible tap end to be inserted into the spark plug port hole. Bearing in mind this unique tool cleans or cuts the thread on the way out. With the collapsible tap end, the tool is inserted past the damaged or contaminated spark plug thread. The expanding rod is replaced through the centre of the ThreadSaver tool and now comes the best part, the ThreadSaver is wound out cleaning or repairing and realigning the thread and with the help of a little grease on the tap end, metal and carbon particles are brought out through the spark plug port hole along with the ThreadSaver tool.
The ThreadSaver is a cheap investment, is simple, and is fast and easy to use. It will go a long way in assisting to reduce lost labor time on a fairly common workshop problem when replacing spark plugs.
A tool that every technician should have, ThreadSaver works on cast iron and alloy cylinder heads, can be used on cars, trucks, motor cycles, marine, lawn mowers, chainsaws or anything that uses a 12mm or 14 mm spark plug. Back to top