Can we talk about how people keep torquing spark plugs wrong on Continentals?

I’ve seen three guys in the last month just crank them down until they feel snug. That’s a one-way ticket to stripping threads or busting the ceramic insulator in the head. On an O-470, the spec is 300 inch-pounds, not a grunt and a half. Has anyone else caught this at your shop or am I the only one keeping a torque wrench handy?

2 comments

2 Comments

robert641mo ago

The last O-470 I worked on had a helicoil in #3 from some guy who thought "good n tight" was good enough. 300 inch-pounds is barely more than hand tight on a 3/8 ratchet, more like a firm wrist turn. I keep a Snap-on inch-pound torque wrench in my box just for plugs and keep the spec card taped to the lid. If you hear that click before it feels snug, stop and check the threads, its better to back it off than force it.

taylor_mitchell801mo ago

Man that helicoil story hits home. I did the exact same thing on a Lycoming years ago, thought I had it torqued right but the plug was stripped by the next annual. Now I just go by feel with a ratchet and stop at that firm snug point, never force it past. And yeah you're totally right about checking threads before cranking down, I ruined a cylinder head once by ignoring that little click early on. I actually switched to antisieze on the threads after that mistake, seems to help the torque read more consistently without surprise problems. Still keep my torque wrench handy for critical stuff but for plugs I trust the wrist method more these days.