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Can we talk about using a torque wrench on spark plugs in a GA engine | Aircraft Mechanics - Vivisector

Can we talk about using a torque wrench on spark plugs in a GA engine

I was doing a routine plug change on a Lycoming last Tuesday and had a choice to make. Either use the beam style torque wrench my old mentor swore by or go with the click type I picked up at a pawn shop for $40. I went with the click wrench because it felt more precise, but I double checked every single plug with the beam wrench anyway. Turns out the click wrench was off by about 8 foot pounds on the low end after the first few cycles. That mismatch could have stripped a plug thread or left one loose enough to back out over time. Now I keep both wrenches in my box and use the beam style as a sanity check on anything critical. Has anyone else run into a click wrench that drifted out of spec without you knowing?

3 comments

3 Comments

lewis.brian4mo ago

Click wrench off by about 8 foot pounds" - that's not a torque wrench, that's just a VERY enthusiastic hand tool with a noise-making feature. I bet the pawn shop guy knew exactly what he was selling.

the_alex4mo ago

Wait, you actually trusted a $40 pawn shop torque wrench on a Lycoming?

pat_murray534mo ago

You say "click wrench off by about 8 foot pounds" like that's a small thing. But on a Lycoming, that's huge. 8 foot pounds is the difference between a stud staying tight and pulling threads right out of the case. I've seen guys strip out cylinder base studs with a wrong torque and it's a full teardown to fix. That pawn shop wrench was probably a cheap cam-over style that never got calibrated properly even when new. Honestly, $40 isn't the red flag. Not testing it on a known good bolt first is where the real mistake happens. When did you last check your torque wrenches against a reference?