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My hangar debate: replacing every seal on engine teardown or just the bad ones?

I've been maintaining piston engines for a few years, and every overhaul brings the same argument. Some shop guys say swap every seal, gasket, and O-ring no matter what. They call it cheap insurance against hidden leaks later. I see their point after engines came back with leaks from seals we thought were fine. But other respected mechanics ask why waste parts and money if a seal looks perfect and passes inspection. They prefer to focus on worn parts and avoid extra waste. My own experience is mixed, with new seals sometimes failing faster than broken-in old ones. So what's your shop's standard? All seals every time, or only when worn?
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3 Comments
gracer28
gracer281mo ago
Go ahead and replace every seal, then watch a new one leak first. Why do we even pretend this is a science? Might as well flip a coin.
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carr.matthew
Can we just agree both sides have a point here?
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baker.ruby
baker.ruby1mo ago
Ugh... is it even worth the fight? Seen plenty of "new" seals weep right away while the old ones were still holding fine. Feels like throwing parts at a problem that might not exist. Sure, a hidden leak is bad, but so is wasting money and time on stuff that ain't broke. If it passes a good check, it's probably fine... engines aren't made of glass.
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