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Caught three guys last month torquing lug nuts dry, please use a dab of grease
I was helping out on a Cessna 172 annual in Tucson last month and watched a newer guy run the main gear nuts down dry with an impact, then wonder why his torque wrench clicked at a number that felt off. Dry threads eat up a big chunk of your torque in friction, so the bolt is not actually getting the clamp load you think it is, and on gear legs that is a bad place to guess. I ran a quick test on a scrap bolt with and without a light coat of moly grease and saw close to a 25 percent difference on the same wrench setting. Check your maintenance manual for what lube it calls out, some say oil, some say grease, some say dry, and it is not the same across every airframe. Anyone got a go to reference for thread lube values they actually trust in the hangar?
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willowg8817d ago
My uncle ran a small shop in Kingman back in the 80s and he kept a coffee can full of nothing but greased bolts for this exact reason. He said a clean dry 3/8 bolt and a greased one would read hours apart on the same wrench, and he had a laminated chart taped inside his toolbox for years. Funny thing is he never trusted the chart either, he would still test every new batch. Tucson heat does not help matters, that impact was probably pulling half its torque from rust and heat alone.
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