|
Because these pages may move to other servers from time to time, we have put this information on our server for all to view. If you are the original author, and you have a problem with that, please contact us and we will remove this page.
Page Provided
By The |
|
ReplacingSparkPlugs?? |
|
Posted by GOrilla on Mon Oct 12 08:10:01 1998: In reply to: Re: Replacing Spark Plugs?? posted by Marty Rood on Mon Oct 12 01:18:00 1998: I'm with Rikki, the tech board has been slow. And I woke up early feeling techy today. I have been doing more of the artsy-fartsy picture stuff and posting ride info on the TXVOA. (Ya'll come by for a visit :) http://www.valhalla-six-guns.com/ Below is a long winded post, just got to typing and created a post on gathered facts and in general what I know about spark plugs. Marty has a good philosophy, if it at broke don't fix it. I generally don't consider changing my everyday vehicle plugs til about the 60k range. My Hi-pro Mustang plugs are changed every 5k miles for reasons I will list below. My Valk has almost 9k miles and I feel they have a ways to go before I will change them, probably around 15k miles or just before I go to Crawford. Not, that I would need to, it's all a matter of personal preference and how I feel about engine performance. My selection of the Valks next plug has yet to be determined. I will probably remain with the stock plugs because they seem to be doing fine. There are a lot of hype plugs out their that claim to increase horsepower and mileage but I have never seen one yet with a good write-up from a outside reputable source. As spark plugs grow older, they lose their sharp edges and material from the center and the ground electrode is slowly eroded away. As the gap between these two points grows, the voltage required to bridge this gap increases proportionately. The ignition system must work harder to compensate for this higher voltage requirement and hence there are a greater rate of misfires, or incomplete combustion cycles. Each misfire means lost horsepower, reduced fuel economy and higher emissions. Replacing worn out spark plugs with new ones (with sharp new edges) effectively restores the ignition system's efficiency and reduces the percentage of misfires, restoring power, economy, and reducing emissions. How long spark plugs last will depend on a variety of factors, including engine compression, fuel used, gap, center/ground electrode material, how the vehicle is used, etc. Installing spark plugs The spark plug performs four main functions: 1. It fills a hole in the cylinder head.(a little levity:) 2. It acts as a dielectric insulator for the ignition system. 3. It provides spark for the combustion process to occur. 4. It removes heat from the combustion chamber. It is important to remember that spark plugs do not create heat, they help remove it. Anything that prevents a spark plug from removing the proper amount of heat can lead to pre-ignition, detonation, premature spark plug failure and even internal engine damage, especially in two stroke engines or modified engines. In the simplest of terms, the spark plug acts as the thermometer of the engine....much like a doctor examining a patient, this "thermometer" can be used to effectively diagnose the amount of heat present in each combustion chamber. With some experience you can interpet the plugs' visual cues and accurately determine the engine's overall operating condition, get a feel for air/fuel ratios, and even diagnose driveability problems. Spark plugs are valuable tuning tools, when interpreted correctly. They will show symptoms of other problems and can reveal a great deal about the engine's overall condition. With common sense and experince you can evaluate the appearance of the spark plug's firing tip and will begin to make a diagnosis or some basic assumptions based on the physical appearance of the spark plugs. Reading spark plugs can be a valuable tuning aid. By examining the Insulator firing nose color, you can determine much about the engine's overall operating condition. In general, a light tan/gray color tells you that the spark plug is at the optimum temperature and that the engine is in good operating condition. Dark coloring, such as heavy black wet or dry deposits usually indicate a fouling problem. Heavy, dry deposits can indicate an overly rich condition, too cold a heat range spark plug, possible vacuum leak, low compression, overly retarded timing, or too large a plug gap. If the deposits are wet, it can be an indication of a breached head gasket, oil control from rings or valvetrain problems, or an extremely rich condition, depending on what liquid is present at the firing tip. One must also look for signs of detonation, such as silver specs, black specs, or melting or breakage at the firing tip. Signs of fouling or excessive heat must be traced quickly to prevent further deterioration of performance and to prevent possible engine damage. Believe it or not torque is one of the most critical aspects of spark plug installation. Torque directly affects the spark plugs' ability to transfer heat out of the combustion chamber. A spark plug that is under-torqued will not be fully seated on the cylinder head, hence heat transfer will be slowed. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. Serious engine damage is not far behind. An over-torqued spark plug can suffer from severe stress to the Metal Shell which in turn can distort the spark plug's inner gas seals or even cause a hairline fracture to the spark plug's insulator...in either case, heat transfer can again be slowed and the above mentioned conditions can occur. The spark plug holes must always be cleaned prior to installation, otherwise you may be torquing against dirt or debris and the spark plug may actually end up under-torqued, even though your torque wrench says otherwise. Of course, you should only install spark plugs in a cool engine, because metal expands when its hot and installation may prove difficult. Proper torque specs for both aluminum and cast iron cylinder heads are listed below. Gapping Since the gap size has a direct affect on the spark plugs' tip temperature and on the voltage necessary to ionize(light) the air/fuel mixture, careful attention is required. While it is a popular misconception that plugs are pre-gapped from the factory, the fact remains that the gap must be adjusted for the vehicle that the spark plug is intended for. Those with modified engines must remember that a modified engine with higher compression or forced induction will typically require a smaller gap settings (to ensure ignitability in these denser air/fuel mixtures). As a rule, the more power you are making, the smaller the gap you will need. A spark plug's voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture, maximizing burn efficiency. It is for this reason that most racers add high power ignition systems. The added power allows them to open the gap, yet still provide a strong spark. With this mind, many think the larger the gap the better. In fact, some aftermarket ignition systems boast that their systems can tolerate gaps that are extreme, be wary of such claims. In most cases, the largest gap you can run may still be smaller than you think. Indexing This is for racers only !! Indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction. However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine...while most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve. In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output...for a 500hp engine, you'd be lucky to get 5hp...while there are exceptions, the bottom line is that without a dyno, gauging success will be difficult. Heat Range Selection Let's make this really simple: when you need your engine to run a little cooler, run a colder plug. When you need your engine to run a little hotter, run a hotter spark plug. However, going to a hotter spark plug can sometimes mask a serious symptom of another problem that can lead to engine damage. Be very careful with heat ranges. Seek professional guidance if you are unsure. With modified engines (those engines that have increased their compression), more heat is a by-product of the added power that normally comes with increased compression. In short, select one heat range colder for every 75-100 hp you add, or when you significantly raise compression. Also remember to retard the timing a little and to increase fuel enrichment and octane. These tips are critical when adding forced induction (turbos, superchargers or Nitrous kits), and failure to address ALL of these areas will virtually guarantee engine damage. An engine that has poor oil control can sometimes mask the symptom temporarily by running a slightly hotter spark plug. While this is a "Band-Aid" approach, it is one of the only examples of when and why one would select a hotter spark plug. Using "racing" spark plugs Be cautious!! In reality, most "racing" spark plugs are just colder heat ranges of the street versions of the street spark plug...they don't provide any more voltage to the spark plug tip!! Their internal construction is no different than most standard spark plugs. There are some exceptions, though. Extremely high compression cars or bikes or those running exotic fuels will have different spark plug requirements and hence spark plugs that are well-suited for these requirements...they are classified as "specialized spark plugs for racing applications". Some are built with precious metal alloy tips for greater durability for their ability to fire in denser or leaner air/fuel mixtures. If you are looking to "screw in" some cheap horsepower , in most cases, spark plugs are not the answer. To be blunt, when experienced tuners build race motors, they select their spark plugs for different reasons: to remove heat more efficiently, provide sufficient spark to completely light all the air/fuel mixture, and to survive the added stresses placed upon a high performance engine's spark plugs, and to achieve optimum piston-to-plug clearance. Some of these "specialized racing plugs" are made with precious metal alloy center/ground electrodes or fine wire tips or retracted-nose insulators...again, these features do not necessarily mean that the spark plug will allow the engine to make more power, but these features are what allow the spark plug to survive in these tortuous conditions....most racers know screwing in a new set of spark plugs will not magically "unlock" hidden horsepower. Using high power ignition systems (or what I know about car ignitions) Many of the more popular aftermarket ignition systems are of the capacitive discharge type. They store voltage, or accumulate it, until a point at which a trigger signal allows release of this more powerful spark. Companies like Mallory, MSD, Crane and Accel, to name a few, offer such systems. They affect spark plugs in that they allow the gaps to be opened up to take advantage of the increased capacity. The theory is that the larger and the more intense the spark you are able to present to the air/fuel mixture, the more likely you will be to burn more fuel, and hence the more power you will make. I have only used hi-pro ignitions on modified or older non-computer controlled vehicles. In reality, computer controlled vehicles do such a good job of lighting off the air/fuel mixture (as evidence by the ultra-low emissions), added ignition capacity would do little to burn more fuel since the stock configuration is doing such a good job. Older non-computer controlled vehicles or those that have been modified with higher compression or boosted (nitrous, turbo, supercharged) engines can certainly take advantage of a more powerful ignition system. Looks like I rambled on for more than my 2 cents worth. GOrilla#22 Addendum Notes From GOrilla Different thread diameter spark plugs require different torque specs. For most 14 mm spark plugs, about 18-22 lb/ft is accurate. Aluminum heads will take slightly less torque than cast iron heads. As a basic rule, for gasket type spark plugs, use 1/2 - 3/4 of a turn after finger tight. For taper seat spark plugs, use only 1/16 - 1/8 of a turn after finger tight. |
ValkyrieRiders.com F6Rider Webzine ShopTalk Just Pics Valkyrie Hot Links
