TIL I've been torqueing spark plugs wrong for 15 years

I was helping a younger mechanic at the FBO in Boise last Tuesday and he pulled out a torque wrench for spark plugs. I told him he was being too careful, just give it the good-n-tight method. He showed me a service bulletin from Continental that said improper torque on spark plugs can cause thread damage in the cylinder head. I looked it up and sure enough, I've been over-torquing mine for years. I checked five of my recent jobs and three were above spec. Anyone else find out they've been doing a basic step wrong for way too long?

3 comments

3 Comments

the_tessa10d ago

Slammed the torque wrench down in my box after reading this and walked over to check my Beechcraft. Yep, every single plug was cranked down like I was trying to seat a water main valve. I feel personally attacked by @christopherh79's story because that's almost exactly what happened to me with a lawnmower once. Snapped a plug and spent a whole Saturday drilling it out while my neighbor watched and drank beer. Guess I'll be that guy with the torque wrench in the hangar now too.

nancyjones10d ago

Huh, I gotta respectfully disagree with you there. I've been doing the good-n-tight method for over 20 years on my own plane and never had a single issue with stripped threads or broken plugs. The factory torque spec is fine for a cold engine on a bench but in the field, a little extra oomph feels right to me (especially if it's a hot engine and you're worried about vibration loosening things up).

christopherh7910d ago

My buddy Rick had a 172 that he was redoing the plugs on a few years back. He swore by the good-n-tight method too, said he learned it from his old man. Well, one hot August afternoon he was torquing down a plug on the left mag and it just... kept going. Snapped the electrode right off inside the cylinder head. Cost him two weekends and a 600 dollar trip to the machine shop to get it helicoiled. I still snug mine by feel but I keep a torque wrench in the hangar now just in case.