Just realized people are overtorquing spark plugs on Lycomings way too much

I keep seeing guys at our FBO cranking down spark plugs on those O-360 engines like they're trying to seat a lug nut. You only need 12-15 ft-lbs on most of them, not 30. I had an engine come through last month that had a cracked ceramic insulator from being too tight, and the pilot reported a rough run-up. Check your torque wrench calibration if you haven't in a while, mine was off by 4 ft-lbs. Has anyone else seen cracked plugs from overtorque or am I the only one?

2 comments

2 Comments

richard_west512d ago

Hey, did you ever hear about that A&P who snapped a spark plug flush inside a cylinder head a couple years back? He was using a beam style torque wrench that hadn't been calibrated since the 90s, ended up having to pull the whole jug. I read a forum thread where a guy tested ten different torque wrenches at his shop and five of them were off by more than 8 ft-lbs on the low end. It's wild how nobody checks those things until something breaks.

parkernelson12d ago

...and the craziest part is beam style wrenches are supposed to be the most reliable since there's no springs to wear out. But if that needle is bent even a little bit or the scale is off, you're just guessing. Ngl I had a similar thing happen on a buddy's motorcycle a few years back. We borrowed my neighbor's old Craftsman beam wrench and it was reading 45 ft-lbs when the fastener was barely snug. I picked up a split beam clicker after that and I check it against a known good wrench every six months on the low end.