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Old timer told me to stop torquing spark plugs with my wrist
Guy with 30 years at Delta said hand tight plus 90 degrees was all you need, I cranked one to spec anyway and cracked the ceramic on a Continental IO-520. Anybody else had that moment where you ignore the graybeard and pay for it right away?
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cameronn621mo ago
The thing nobody's mentioned yet is that hand tight plus 90 degrees assumes a clean, dry thread with no anti-seize. If that old timer was running a wet torque or had some residue on the threads, the rotational friction changes completely and you'll overtorque every time. I've seen guys snap head bolts on small block Chevys because they put anti-seize on but still used the dry torque spec. That 90 degrees of rotation moves way more linear distance when things are lubed up. Plus on aircraft engines they often use new copper gaskets that crush differently than used ones. So the real variable is thread condition, not just the angle.
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bennett.nora1mo ago
Your mileage may vary big time on that old timer advice. Hand tight plus 90 is actually pretty standard for some aircraft engines, but it depends on the gasket type and surface condition. The real lesson is always trust the manual for your specific setup, not some general rule from a retired mechanic.
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blair5971mo ago
Man, that's exactly the kind of thing that bit my buddy Dave last summer. He was rebuilding an old Ford 300 inline six for his truck, and some YouTube "expert" swore by the hand tight plus a quarter turn method for the manifold bolts. Dave figured it was fine, skipped checking the actual spec in the manual, and wound up snapping two bolts clean off because the manifold was a different casting than what the guy was using. Had to drill and extract those, what a nightmare.
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