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Showerthought: people keep torqueing spark plugs like they're lug nuts and it's wrecking cylinder heads
Pulled the plugs on a Bonanza last Tuesday and two of the eight came out with aluminum threads stuck to them, because the last guy torqued them to what felt right instead of using a torque wrench. Lycoming says 35 foot pounds on a 3/8 plug and people still crank them down to 50 plus, then the head cracks at the boss and now you're looking at a cylinder change instead of a $12 plug. I've seen this four times this year at our shop in Spokane, and every single owner says the same thing, that they just snugged it good. Copper anti seize changes the number too, and nobody ever accounts for that when they guess. Who else is seeing crushed gaskets and pulled threads on a regular basis, and do you use a torque wrench on every plug or just the ones that are hard to reach?
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stone.lisa1mo ago
Just snugged it good" is how every one of these stories starts, and it always ends with a helicoil kit. Copper anti seize is the sneaky part, that stuff can cut torque by 20 percent easy, so the guy patting himself on the back for using a wrench is still over stretching the threads if he's going by the book number dry. Torque wrench on every single plug, even the back two on a Bonanza where you're working blind and upside down. Thirty five foot pounds is a real number, not a vibe. Your hand has no calibration sticker on it.
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