Kwik-fit and a puncture.
in [Car Maintenance]
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From: Chris Whelan on 10 Nov 2009 16:39 On Tue, 10 Nov 2009 21:36:32 +0000, Duncan Wood wrote: [Missing tags added] <Pedant> > Most engines still have overhead valves:-) But not many need re-torquing > nowadays. </> :-) Chris -- Remove prejudice to reply.
From: Mrcheerful on 10 Nov 2009 16:43 Paul wrote: > Mrcheerful wrote: >> Paul wrote: >>> Mrcheerful wrote: >>>> Paul wrote: >>>>> 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.... >>>> you need far more force to undo, mainly because of friction and >>>> corrosion, using a torque wrench to undo would not give a >>>> meaningful result and might overload and damage the accuracy of >>>> the torque wrench. in addition most people do not understand how >>>> to use a torque wrench to re-check the tightness of a bolt. >>>> >>>> >>> Corrosion aside, that just seems to be 'anti' common sense.. >>> >>> Tightening, you are overcoming (increasing) friction and trying to >>> make a piece of steel longer than it wants to be - so two components >>> to the force in Nm required to get the nut to where you want it. >>> >>> Loosening, you need to overcome the same friction (decreasing) but >>> do not have the stretching element of the material.. >>> >>> So in principle, if you tighten up new, greased nuts on a thread and >>> then immediately take them off using a torque wrench - it should >>> take less effort? >>> This just seems so obvious, i can see I'm going to have to have a go >>> to test the theory. ;-) >> >> the friction is the problem, when tightening you have the mating >> surfaces already sliding and it easier to keep them sliding than it >> is to re-start them sliding, especially in the opposite direction, >> the metal itself acts a bit like a one-way clutch. >> How about this for an analogy: Imagine two pieces of spiky carpet >> (giant size version of the faces of the nut and wheel) if you were >> to rotate and compress the carpet then the fibres would all get >> squashed and interlock, to undo in the opposite direction you have >> to overcome the bent fibres and get them going the other way. >> >> > Ah ok, I was considering the fact that some low torque is used to get > the carpets closer togther , then bigger torque to lock. Sensibly the > same torque would then be needed to break the bond, and then a much > lower than low torque to continue as you are then just spinning the > nut rather than parting the objects. > > This I found intersting: > http://www.hexagon.de/tasignat.htm > > > "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.
From: Charles C on 10 Nov 2009 16:46 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! :-)
From: Mrcheerful on 10 Nov 2009 16:48 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?
From: Duncan Wood on 10 Nov 2009 16:55
On Tue, 10 Nov 2009 21:43:11 -0000, Mrcheerful <nbkm57(a)hotmail.co.uk> wrote: > Paul wrote: >> Mrcheerful wrote: >>> Paul wrote: >>>> Mrcheerful wrote: >>>>> Paul wrote: >>>>>> 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.... >>>>> you need far more force to undo, mainly because of friction and >>>>> corrosion, using a torque wrench to undo would not give a >>>>> meaningful result and might overload and damage the accuracy of >>>>> the torque wrench. in addition most people do not understand how >>>>> to use a torque wrench to re-check the tightness of a bolt. >>>>> >>>>> >>>> Corrosion aside, that just seems to be 'anti' common sense.. >>>> >>>> Tightening, you are overcoming (increasing) friction and trying to >>>> make a piece of steel longer than it wants to be - so two components >>>> to the force in Nm required to get the nut to where you want it. >>>> >>>> Loosening, you need to overcome the same friction (decreasing) but >>>> do not have the stretching element of the material.. >>>> >>>> So in principle, if you tighten up new, greased nuts on a thread and >>>> then immediately take them off using a torque wrench - it should >>>> take less effort? >>>> This just seems so obvious, i can see I'm going to have to have a go >>>> to test the theory. ;-) >>> >>> the friction is the problem, when tightening you have the mating >>> surfaces already sliding and it easier to keep them sliding than it >>> is to re-start them sliding, especially in the opposite direction, >>> the metal itself acts a bit like a one-way clutch. >>> How about this for an analogy: Imagine two pieces of spiky carpet >>> (giant size version of the faces of the nut and wheel) if you were >>> to rotate and compress the carpet then the fibres would all get >>> squashed and interlock, to undo in the opposite direction you have >>> to overcome the bent fibres and get them going the other way. >>> >>> >> Ah ok, I was considering the fact that some low torque is used to get >> the carpets closer togther , then bigger torque to lock. Sensibly the >> same torque would then be needed to break the bond, and then a much >> lower than low torque to continue as you are then just spinning the >> nut rather than parting the objects. >> >> This I found intersting: >> http://www.hexagon.de/tasignat.htm >> >> >> "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. > > It's much more accurate being the main difference. |