Common Issues Faced by Engine Spark Plugs

The spark plug is an essential component of countless aircraft engines, providing the sparks necessary for igniting fuel-and-air mixtures. Engine malfunctions are commonly attributable to a faulty spark plug, often resulting from a number of conditions that affect such components. To prevent the inefficient operation of spark plugs or their outright failure, aircraft owners should carry out regular inspections and maintenance practices. In this blog, we will discuss the most common causes of faulty spark plugs, allowing you to best care for your engine and its components.

Carbon fouling is a common source of failing spark plugs, caused by mixtures that are either too rich or lean. Too rich of mixtures can prevent proper burning, while lean mixtures result in intermittent firing. Every time that the spark plug fails to fire, fuel and oil will begin to collect on the electrodes and nose insulator. To remedy improper fuel and air mixtures, one should check for improper idle mixture adjustments, malfunctioning carburetors, or leaking primers. Rich mixtures can also be determined by the presence of soot or black smoke emitting from exhaust.

Another common source of spark plug fouling is when oil is drawn into the cylinders, passing the piston rings, valve guide components, and impeller shaft oil seal rings. Such issues can even occur with optimal idling fuel and air mixtures, presenting a risk of shorting out the spark plug if the oil is allowed to mix with soot. When oil mixes together with soot, it causes the formation of a solid substance within the chamber. While the issue may clear out on its own after a duration of engine operation, there is always a chance that the spark plug will remain unable to arc the gap between electrodes.

If an engine operates through the use of leaded fuels, the spark plugs are at risk of lead fouling. Lead is often added to aviation fuel for the means of increasing anti-knock qualities, but its presence can create lead oxide during the combustion process. When lead oxide begins to solidify onto the surfaces of the ignition system combustion chamber, its conductive properties may cause misfiring. In order to prevent such formations, ethylene dibromide is commonly added to fuel mixtures. Combining with lead found within the spent fuel, the resulting chemical reaction prevents major formations from establishing. While the emergence of lead oxide may occur with any power setting, the highest chance of formation tends to occur when burning lean mixtures during cruising speeds.

As a common issue faced by all spark plugs, gap erosion can cause the failure of igniting mixtures. Each time a spark is formed across a gap, a part of the electrode is removed from one and deposited on the other. As this process continues over time, the gap between the electrodes constantly increases. Increased gap sizes require higher voltages from the magneto to cross, eventually running the risk of discharging a spark at a weak insulation section of the ignition system. With an overly large gap, common issues such as insulation breakdown, carbon tracking, or premature flashover may occur.

Beyond such examples, there are numerous other spark plug issues that operators should always look out for. When removing spark plugs for maintenance, it is important to disconnect the ignition harness lead and to use proper tooling. At Unlimited Purchasing Services, we can help you secure all the ignition system components and tools that you need for your maintenance endeavors with competitive pricing and rapid lead-times. If you would like to receive quotes on items for your comparisons, fill out and submit an Instant RFQ form on our website and a dedicated account manager will reach out to you in 15 minutes or less. Get started today and see how Unlimited Purchasing can help you fulfill all your operational needs quickly and easily.


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