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

Simon Bennett · 2026-03-02T19:01:50.738184+00:00

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?

gracer287mo 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.matthew7mo ago

Can we just agree both sides have a point here?

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baker.ruby7mo 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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