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Shoutout to the old timer who told me to stop using anti-seize on spark plugs
He said it would foul the threads and cause a loose fit after two heat cycles, and sure enough I had a plug shoot out of a Lycoming cylinder on a Cessna 172 last month at the worst possible moment, has anyone else run into this issue adjusting their torque specs for dry threads?
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michaeljones6d ago
...and that's exactly why I never use anti-seize on anything in an aircraft engine anymore. I learned that lesson the hard way too, but on a car engine years ago. The problem is torque specs are written for dry threads, and when you put that anti-seize in there you're basically lubing up the threads and throwing the torque reading way off. You end up overtorquing the plug into the hole and then it loosens up later from the heat cycling. I've had better luck just running them in dry with a tiny bit of oil on the threads if they're really tight, but even then I'm careful not to overdo it.
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benflores6d ago
Wait, are you saying the anti-seize made the plug shoot out, or the lack of it? I've been using a light coat of anti-seize on aircraft plugs for 15 years and never had one back out. Every A&P I've talked to says the real issue is people slathering it on too thick or using the wrong kind. Torque specs for dry threads are already low on aluminum heads, and adding anti-seize just means you gotta back it off 10-15%. If you go by the book with anti-seize on those Lycoming cylinders, you'll actually end up under-torquing them and they'll loosen up from vibration. I think the old timer might've been right for his situation but it's not one size fits all.
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