Over the last several years, there have been incidents of pre-ignition in large displacement Continental engines. In many cases, it was suspected that cracked or broken ceramic insulators on Champion Aerospace fine wire spark plugs were to blame. The issue led to Cirrus issuing a service bulletin for spark plug applications on its turbocharged models, as did Tornado Alley Turbo, for its aftermarket turbo-normalizing mod.
Subsequently, it turned out the problem wasn’t isolated to turbocharged engines—even normally aspirated engines were damaged.
It was initially theorized that lean-of-peak engine operation (advocated by some manufacturers) might be the culprit of detonation-induced cracking of the plug’s ceramic insulator.
Technically, if done properly, running lean of peak gives the engine a wider detonation margin than rich-of-peak might. Still, Champion kept an open mind and vowed to get to the bottom of the issue.
Without announcement, last year it redesigned both its massive and fine wire aviation spark plugs, while revamping its manufacturing process. While there simply isn’t enough real-world data to point to a definitive fix, we set out to determine if Champion specifically redesigned the plugs to be as reliable as plugs from competitor Tempest.
SPARK PLUG 101
It has long been acknowledged that pre-ignition is the most destructive combustion process in a piston engine. How destructive? Consider that pre-ignition generates enough damaging heat in the cylinder that it can actually melt the piston and rings. You don’t have to be an engine expert to understand the significance of a compromised spark plug. But you do need to understand how a spark plug functions, and the importance of the insulator.
Insulating the central electrode from the outer portion of the spark plug, the insulator keeps much of the heat from the inside of the spark plug away from the fuel/air mixture.
When that electrode breaks, it can allow combustion of the fuel/air mixture ahead of the plug firing. Once pre-ignition is underway, you might see a substantial increase in CHT on the affected cylinder (and sizable levels of vibration), making a good argument for even a basic graphic engine monitor.
Massive electrode spark plugs use two large grounding electrodes on each side of the center electrode, while fine wire plugs have a single, small-gauge grounding wire in the center—making them more fragile during installation.
Drop any plug to the floor from cowling-high and chances are it will stress or break the electrode. The potential for installation damage was another theory behind the insulator problem with Champion’s plugs, as was the theory of thermal shock during large power reductions.
The graphic on page 17 offers an overview of the newly designed massive plug (its cutout looks identical to a fine wire), but Champion’s Kevin Gallagher told us the redesign was as much about executing a new manufacturing process as it is a product improvement, producing an aviation spark plug with internals that closely resemble that of an automotive plug.
He noted that Champion is the only aviation spark plug maker to manufacture its own ceramic insulators and glass seals, while pressing and firing its own cores. Manufacturing is accomplished at Champion’s Liberty, South Carolina, facility.
For its new aviation spark plugs, Champion transitioned from the mechanical stack of a silicon carbide resistor, spring and terminal assembly, to the more modern method that Champion has been using on automotive plugs for many years, consisting of a conductive glass core called a fired-in suppressor seal, or FISS.
Gallagher said that while massive-design plugs represent nearly 95 percent of the market, the design change was made to both its fine wire and massive plugs.
Field Reports
We spoke with a few mechanics to get a feel for their confidence level in the new fine wire plugs, but few were even aware of Champion’s redesign.
One tech, an experienced IA at a busy shop and owner of an IO-550-modified Bonanza, isn’t convinced that Champion had a design flaw at all. He acknowledged that some pilots are pretty rough on their engines, theorizing that it’s tough to pin the blame on Champion’s fine wire plugs, even though Tempest’s fine wire plugs have a better track record in some applications.
We asked Champion’s Gallagher if the redesigned insulator and the new manufacturing process make them less prone to cracking—whether that cracking is caused by thermal shock, water ingestion (in seaplane operations), a lean mixture or the so-called “big pull.” That’s where the risk of detonation increases when an engine lingers in the slightly rich-of- peak zone for too long of a period.
“Throughout the years, Champion has routinely gone through design improvements, while introducing technological advancements, including platinum, and more recently, iridium electrodes. We re-engineered both the design and the manufacturing method used for the ceramic core in our massive and fine wire aviation spark plugs. Hopefully the awareness that has spread through the flying community regarding the dangers of detonation during transition from rich of peak to lean of peak has decreased the incidents of broken insulators in plugs from all manufacturers,” Gallagher told us.
We asked George Braly at Tornado Alley Turbo if Champion’s new design instills enough confidence for him to recommend Champion fine wire plugs in turbo-normalized engines. Braly’s personal opinion is that the problem was isolated to certain batches of fine wire plugs.
“We saw evidence in our shop that the problem was production-batch related. Until I see evidence otherwise, I’m going to assume Champion solved the problem with this redesign,” Braly said.
Braly reinforced the theory that broken ceramics won’t always cause pre-ignition. If a ceramic piece separates from the plug and goes out the exhaust valve, it generally won’t have the damaging effect as if it lodges in the spark plug, effectively becoming a glow plug as the ceramic gets hot.
Braly and the mechanics we spoke with praised Champion for a company that clearly knows how to build spark plugs, given its long history.
It’s important to note that the ceramic in Champion’s massive plugs haven’t shown evidence of cracking. This shouldn’t be confused with Champion’s earlier spark plug resistor problem, which might cause engine roughness, stubborn starting and excessive magneto drops.
With an insulator that closely resembles that used in a Tempest plug, plus a redesigned resistor, it’s still too early to tell if it’s a cure-all for prior problems, but we give Champion credit for being innovative. We’ll offer a long-term report as more of the new spark plugs enter service. Contact www.championaerospace.com.
