Spent 3 years torquing spark plugs wrong before a senior mechanic called me out on it

I was at ExpressJet back in 2017 doing a routine 100-hour on a CRJ200, and I had this habit of just torqueing the spark plugs to the spec number and calling it done. One day, this old timer, Larry, walked by my bay and watched me for maybe 10 seconds before he said "you're gonna crack that cylinder head doing it that way." Turns out I was never lubing the threads lightly with anti-seize before installing them, so my torque values were way off because of the dry friction. He showed me how the manual even mentions it in the fine print on page 42, which I had obviously skimmed right past. I felt like an idiot, but after I started doing it his way, I never had a plug back out or seize up again. Has anyone else had a basic step like that slip by you for way too long?

2 comments

2 Comments

christopher_west11mo ago

Yo did that manual actually have the anti-seize step on page 42 or was Larry just messing with you? I swear I read something similar in a car forum about engine builders always hitting the threads with a tiny bit of anti-seize to get the right clamp force. It makes sense though, dry torque vs wet torque are totally different numbers and can throw off your whole job. I bet half the guys out there are skipping that step and just getting lucky.

jason_robinson1mo ago

Man I ran into that exact thing on a Cummins rebuild last year. The manual said "light coat of anti-seize on bolt threads" but didn't give a torque reduction factor - I had to call a buddy who builds race engines to get the number. Wet torque is usually about 15-20% lower than dry, so you gotta back off your setting or you'll over-stretch the bolt. Did you ever figure out what Larry was actually recommending?