In 1860 tienne Lenoir used an electric spark plug in his first internal combustion engine and is generally credited with the invention of the spark plug.
Early patents for spark plugs included those by Nikola Tesla (in U.S. Patent 609,250 for an ignition timing system, 1898), Frederick Richard Simms (GB 24859/1898, 1898) and Robert Bosch (GB 26907/1898). But only the invention of the first commercially viable high-voltage spark plug as part of a magneto-based ignition system by Robert Bosch’s engineer Gottlob Honold in 1902 made possible the development of the internal combustion engine. Subsequent manufacturing improvements can also be credited to Albert Champion, the Lodge brothers, sons of Sir Oliver Joseph Lodge, who developed and manufactured their father’s idea and also Kenelm Lee Guinness, of the Guinness brewing family, who developed the KLG brand.
Spark plugs come in two basic varieties: cold and hot. Cold plugs work best in high-horsepower high-compression engines. They have less insulation, so more heat can be transferred away from the combustion chamber to the outside of the engine. This is no laughing matter: If the plug isn’t cold enough for a particular application, it can’t get enough heat out of the piston chamber. This can lead to pre-ignition, knocking, and permanent engine damage. If you aren’t sure which spark plug heat range to use, err on the side of using a plug that’s too cold rather than a plug that’s too hot.
Standard spark plugs in modern engines have a copper center electrode core surrounded by a nickel alloy, which you can see at the tip of the plug. Inside the plug, the center electrode is encased in porcelain, which helps transfer heat from the engine to the cooling system.
Premium spark plugs make use of precious metals, like platinum or iridium, in place of the nickel alloy. These metals have higher melting points — and higher prices to match.
Whatever the configuration of your engine, it may very likely have aluminum cylinder heads. If that is the case, make sure you remove and reinstall the spark plugs when the engine is cool. It doesn’t have to be cold, but it shouldn’t be warm and most definitely not hot. Trying to remove the spark plugs while the engine is hot could very likely result in damaged threads in the soft aluminum cylinder heads. Repairing the damage could require removing the cylinder heads or at worst, replacing them. Replacing the cylinder heads is a very expensive and time-consuming job.
The length of the threaded portion of the plug should be closely matched to the thickness of the head. If a plug extends too far into the combustion chamber, it may be struck by the piston, damaging the engine internally. Less dramatically, if the threads of the plug extend into the combustion chamber, the sharp edges of the threads act as point sources of heat which may cause preignition; in addition, deposits which form between the exposed threads may make it difficult to remove the plugs, even damaging the threads on aluminium heads in the process of removal. The protrusion of the tip into the chamber also affects plug performance, however; the more centrally located the spark gap is, generally the better the ignition of the air-fuel mixture will be, although experts believe the process is actually much more complex and dependent on combustion chamber shape. On the other hand, if an engine is “burning oil”, the excess oil leaking into the combustion chamber tends to foul the plug tip and inhibit the spark; in such cases, a plug with less protrusion than the engine would normally call for often collects less fouling and performs better, for a longer period. In fact, special “antifouling” adapters are sold which fit between the plug and the head to reduce the protrusion of the plug for just this reason, on older engines with severe oil burning problems; this will cause the ignition of the fuel-air mixture to be less effective, but in such cases, this is of lesser significance.
The next step would be to gap all the new spark plugs. Make sure that the gap is equal on all the plugs and that it is set to the manufacturer’s specifications. During this procedure, you should also make sure that the outer electrode is centered as evenly as possible over the center electrode.
After the plugs are gapped, then you should take a small amount of the anti-seize compound you purchased and apply it to the bottom two threads of the new spark plugs. Make sure you use a small amount and only apply the compound to the bottom two threads.
Reconnect any of the spark plug boots or ignition coils you may have removed and start the vehicle and make sure it doesn’t miss-fire. Once you’re sure the vehicle is idling and running properly, take the vehicle out for a test drive. It is important to operate the vehicle under a normal and a heavy load to determine if the plugs are indeed operating as designed. Once you are satisfied that everything is OK then return to your shop.
The Barrie Home Inspector drives over 40 K a year and uses Champion Platinum spark plugs in his vehicle. He has found that changing his spark plugs every year gives better gas mileage and he has yet to have his vehicle start, even on the coldest mornings.