We’ve been analyzing spark plugs for a few months now. From this analysis, we’ve found a continuing problem with Champion brand spark plugs. Fine wire plugs seem prone to insulator cracking after a few hundred hours in service. At first, we believed the problem was confined to Tornado Alley Turbo equipped engines. That was probably because those planes fly a lot, so we see them at 100 hour intervals several times each year. TAT’s September 2011 service bulletin #SB11-05 calls for removal of Champion fine wire plugs from their engines.
Now we are seeing this same problem occurring in the lower compression TSIO-550-K engine in the 2011-2012 SR22T. Here is a set of Champion RHB32S plugs with 400 hours since new. You’ll note they have higher than normal resistance readings, and three of them have cracked insulators. Two of them are missing large pieces of insulator, which had to exit the cylinder via the exhaust valve.
Note the un-even resistance readings, on spark plugs that are only 18 months old. This engine was misfiring during climb, and occasionally during cruise. The number two top spark plug insulator is cracked, but hasn’t lost the loose piece yet.
The plugs with 484,000 and 668,000 ohm readings test fine on a bench tester, but cause random misfiring in the engine. It’s difficult to conduct lean of peak operations when the spark plugs mis-fire. That wastes a lot of fuel when you can’t run the engine properly. The two cracked plugs are missing large pieces of nose insulator. The hard ceramic has to depart the cylinder through the exhaust valve. Hopefully without causing any damage on the way…
Here we have the number two cylinder, bottom spark plug. Note the large chunk of insulator that is gone!
So here we have the worst of both problems: broken insulators, and high resistance. The former can cause pre-ignition and engine damage, the latter can cause rough running and that sudden shake that really gets your attention in IMC, over water, or at night.
The next photo is of a 3 year old Champion RHB32S fine wire spark plug removed from a normally aspirated Cirrus SR22 with 675 total hours. Notice that the insulator is not just cracked, but shifted upwards. This is about to lose the entire half of insulator all the way into the spark plug core.
Moving along, let’s look at some nine year old, 1000 hour Champion fine wires removed from a normally aspirated Cirrus SR22. The electrodes are still quite serviceable, and should be, as these plugs should last 2000 hours. This customer had random CHT and EGT problems, particularly on his #2 cylinder. That cylinder’s EGT was running 200 degrees below normal, because both plugs were barely working.
Here you see that four plugs read “open” with a multi-meter. The others are 241,000 and 222,000 ohms, so the magneto has to work very hard to push any spark through these plugs. This engine was very hard to start.
Five out of six of the bottom spark plugs read open. And the remaining one is 438,000 ohms. That’s a lot of spark energy lost to the resistor inside the plug. I’d prefer that the spark pass through to the electrodes, where it will do some good. Fortunately, none of these have cracked electrodes. But look at the deposits and oil in the next photo:
Here you can see the lead and oil deposits in the spark plugs. Fouled spark plugs cause cylinders to pump oil through the rings. Replacing these plugs restored the engine’s performance and cut the oil consumption back to normal. Unfortunately, the standard response to plugs like this, would be to clean the plugs, bench test them, and put them back in the engine. When they foul again, you’d be blaming the cylinders and planning a top overhaul. After all, the bench “bomb tester” says they are good to go. But the center electrode resistance check reveals just how bad these plugs are. Throw them out, and install a new set of spark plugs! You’ll be glad you did.
Here is only a partial collection of defective spark plugs accumulated, since we started analyzing spark plugs just a few months ago. Several dozen were already disposed of before this photo was taken. Most of these plugs are less than 3 years old, but were removed due to cracking and mis-firing problems. Champion fine wire plugs were always promoted for their long life, but that is not the case with these plugs. At $85 each, you’re looking at $15,000 worth of spark plugs that didn’t make it past 700 hours (on average) in service.
Stay tuned for more analysis as we report back on the engines running Tempest fine wire spark plugs. We’ll look at how the plugs are aging, and how the engine data compares since changing over. Based on initial reports, we’re expecting lower fuel and oil consumption, and more stable EGT and CHT readings.
There are two things we can learn from this problem:
1- A cracked insulator can develop at any time, and it can become a glow plug with out warning. If your CHT rapidly rises above 500 degrees, go full rich, retard power as much as possible, and land.
2- High resistance is not directly related to insulator cracking. It simply makes your engine run poorly, consume more fuel, and damages magnetos & ignition harnesses.
Here’s a great video on how Tempest makes their spark plugs, in the USA:
Part three to follow soon!
Part one is here: http://www.flyplatinum.com/blog/?p=690
UPDATED 4-11-2012 WITH 2008 SR22 NON-TURBO CRACKED PLUGS:
This next set of plugs was removed yesterday from a 2008 Cirrus SR22, normally aspirated airplane with 777 hours since new. We see this plane for 50 and 100 hour inspections so we are very familiar with it. At the last 100 hour inspection at the end of January, the plugs were tested and three were replaced due to cracking. Now, 100 hours later, we have three more cracked. Even more noteworthy, one of the three new plugs already has 42,000 ohms of resistance.
All of these plugs tested below 5,000 ohms only 100 hours ago.
Three of the top plugs are cracked. Two are missing large chunks, and one is broken but the piece hasn’t worked it’s way out yet. Only the wire is keeping it from being eaten by the cylinder.
It’s not the best situation when you can’t trust your spark plugs.