Kwik-fit and a puncture.
in [Car Maintenance]
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From: Charles C on 10 Nov 2009 17:11 Mrcheerful wrote: > Charles C wrote: >> Harry Bloomfield wrote: >>> Paul explained on 10/11/2009 : >>>> Harry Bloomfield wrote: >>>>> Dave Plowman (News) used his keyboard to write : >>>>>> BTW, congrats to Audi for giving the wheel bolt torque in the >>>>>> driver's handbook. 120 Nm If only they took their own advice - it >>>>>> was nowhere that >>>>>> tight when I took it off. >>>>> They can settle in a little, especially so on a new car. The advice >>>>> is to recheck them after a period. >>>>> >>>> Am I being daft - or does it not take less force to UNDO a nut than >>>> to tighten it? If it takes 120 Nm to get as tight as you like, does >>>> it take 120Nm to get it undone again? Not something I've ever >>>> tried, but its never occurred to me to use a torque wrench to undo >>>> a nut.... >>> I would suggest that if undone straight away, that it would take a >>> little less. However if left for some time and especially if there is >>> corrosion, it can take more effort to undo them. >>> >> Bingo! >> >> :-) > > who undoes a bolt straight away? > > I must be the only person that had to fit, e.g. a wheel, only to remove it a couple of days later :-) I must have been too impoverished in my younger days, get the car running, get the parts, then repair. Talking about wheels, once they have been on the car for a while the threads seize a bit on the hub (assuming the car has bolts), and also the bolt itself can seize nicely on the fase of alloy wheels. That means. a lot of force is needed to undo the bolts (or air impact tools which you .probably use most of the time ... good on you). Surely you must have had wheels stuck on hubs (esp. alloy wheels) why not the bolts or nuts being stuck the same way :-) However, I agree with you, even if I don't grasp the essence of it, it feels as if less force is needed for torquing than for undoing a bolt, even it has just been tightened. Going back to the OP's comment, the bolts might have been loose or there was no "crunch" when they were undone because they had not been on long enough. Charles
From: Mrcheerful on 10 Nov 2009 17:34 Charles C wrote: > Mrcheerful wrote: >> Charles C wrote: >>> Harry Bloomfield wrote: >>>> Paul explained on 10/11/2009 : >>>>> Harry Bloomfield wrote: >>>>>> Dave Plowman (News) used his keyboard to write : >>>>>>> BTW, congrats to Audi for giving the wheel bolt torque in the >>>>>>> driver's handbook. 120 Nm If only they took their own advice - >>>>>>> it was nowhere that >>>>>>> tight when I took it off. >>>>>> They can settle in a little, especially so on a new car. The >>>>>> advice is to recheck them after a period. >>>>>> >>>>> Am I being daft - or does it not take less force to UNDO a nut >>>>> than to tighten it? If it takes 120 Nm to get as tight as you >>>>> like, does it take 120Nm to get it undone again? Not something >>>>> I've ever tried, but its never occurred to me to use a torque >>>>> wrench to undo a nut.... >>>> I would suggest that if undone straight away, that it would take a >>>> little less. However if left for some time and especially if there >>>> is corrosion, it can take more effort to undo them. >>>> >>> Bingo! >>> >>> :-) >> >> who undoes a bolt straight away? >> >> > > I must be the only person that had to fit, e.g. a wheel, only to > remove it a couple of days later :-) I must have been too > impoverished in my younger days, get the car running, get the parts, > then repair. > Talking about wheels, once they have been on the car for a while the > threads seize a bit on the hub (assuming the car has bolts), and also > the bolt itself can seize nicely on the fase of alloy wheels. That > means. a lot of force is needed to undo the bolts (or air impact tools > which you .probably use most of the time ... good on you). Surely you > must have had wheels stuck on hubs (esp. alloy wheels) why not the > bolts or nuts being stuck the same way :-) > > However, I agree with you, even if I don't grasp the essence of it, it > feels as if less force is needed for torquing than for undoing a bolt, > even it has just been tightened. Going back to the OP's comment, the > bolts might have been loose or there was no "crunch" when they were > undone because they had not been on long enough. > > Charles I am often frustrated when attempting to undo wheel nuts, the air impact wrench I have is rated at 600 lb ft in reverse, yet sometimes cannot undo a wheel nut put on by some monkey at a tyre shop. It is often necessary to get out the big bar and 4ft scaffold pole, which I do not believe was used to do them up!! Therefore there is more power needed to undo than to do up.
From: Chris Bartram on 10 Nov 2009 17:41 Mrcheerful wrote: > in addition most > people do not understand how to use a torque wrench to re-check the > tightness of a bolt. > > Presumably slacken it and re-tighten, or am I missing something?
From: Paul on 10 Nov 2009 17:49 Mrcheerful wrote: >> "In one release angle study, a part had a tightening angle of 120 >> degrees. Once the part sat overnight, the release angle was 20 >> degrees. The vendor was already aware there was a major problem >> because the parts were falling apart. >> The study showed that relaxation in the threads was causing an >> approximately 80% loss in clamp force over a 12 hour period. The >> release angle method provided a quantitative answer as to how much >> clamp force was being lost and clearly showed that there had to be a >> redesign of the parts." >> >> which must have a bearing on the original question. > > angle tightening is rather different to torque tightening. > > Yes, but the point was that (poorly designed) components can give after a relatively short period of time - without external influences.
From: Mrcheerful on 10 Nov 2009 18:02
Chris Bartram wrote: > Mrcheerful wrote: >> in addition most >> people do not understand how to use a torque wrench to re-check the >> tightness of a bolt. >> >> > > Presumably slacken it and re-tighten, or am I missing something? that is the right way, many people just try to apply the original torque without the slacken first bit. |