MGC News – October 2020
MGC conversations with Richard Mixture, October 2020
Do You Grease Your Nuts?
Hello again, it’s Richard here. Have you ever greased your nuts? Someone asked me a similar question recently, “Would you ever run your engine without oil?” Of course not, what a stupid question. Then his next question was “Have you ever greased your nuts and bolts before you tighten them up?” I thought about it for a moment. Maybe his first question wasn’t so stupid after all. He made a good point, so I decided to find out more.
The subject came about when I was replacing a rear hub and bearing in the old girl, she’ now 51 years old you know? The manual specified tightening the axle nut up to 150 ft lbs (204 nm – what does ‘nm’ mean anyway?). I grabbed my torque wrench and it only went up to 120 ft lbs (163nm). Hmm, what was I going to do? A bit of water pipe might help?
I like to sleep on things, so after a little nap in the old wing back, I thought to myself, I wonder how much friction in the thread between the axle and the nut, and between the nut and washer was stopping the nut being torqued up to its specification. So, lubrication sounded like a good thing to do. I decided to consult my wise old neighbour who’s done a bit of engineering in his time, and he asked me “do you grease you nuts Richard? Oh, I thought, I was thinking oil, but maybe grease would be better? Should it be a high-pressure grease?
I was in a quandary. What do I use?
Richard, he said “When you torque up a bolt, you create tension in the bolt, which in turn creates a perpendicular force that clamps the things that you are bolting together. Over 40% of the torque used to tighten up your nuts can be taken up by friction. A specified torque has to translate into a desired clamping force, so if friction is taking up a lot of the torque, you won’t get to the desired force.” I other words it won’t be tight enough.
I was told that torqueing up a nut to apply a certain force depends on the thread used and if it’s worn or not, the material used to make the nut (and axle in this case), its’ finish, the mechanic’s ability to apply the torque … Stop!!! All I want to do is tighten up a NUT! Evidently, you get more consistency tightening up lubricated nuts than you do with dry nuts. This is starting to sound like a squirrel’s paradise.
Some lubricates are designed to work under high pressure and some work better at low pressure. I thought that 150 ft lbs would probably apply a lot of force to the axle so a high-pressure grease might be best. If the nut and axle is likely to need servicing at any time, then a good quality anti-seize grease would work. Also consider that in high temperatures a poor quality grease can lose its’ lubrication qualities over time. Anti-seize lubricants traditionally use nickel, zinc, copper or lead and may contaminate an engine or gearbox let alone the environment or your personal health. Then consider galvanic corrosion between different metals such as stainless steel, aluminium, bronze or brass nuts and the anti-seize. If this may be a problem then consider a non-metallic based anti-seize.
Sometimes, the manufacturer actually specifies a lubricate to be used. In this case you better do as you’re told!
Blimey, all I wanted to do is tighten one nut on the axle of my MGC!
I better ‘fess up and say I did use a piece of waterpipe to extend the handle of my torque wrench in order to line up the castellations in the nut with the hole in the axle so that the spit pin could be inserted. Is that near enough? NO! It’s best to use a 150 ft lbs torque wrench.
Torsion Bar Run
Now MGCers et al, with any luck the sun will be shining, the blossom’s blooming and the bees buzzing so it’s time for an MGC run, put Saturday 31st October in your diary and we’ll meet at 1.30pm at Beaumont Road, Adelaide, just off Greenhill Road.
Remember ladies and gentlemen keep ‘em tuned and stay well, stay very well!