Kwik-fit and a puncture.

#21

Paul explained on 10/11/2009 :

Quote:

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.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

#22

Mrcheerful laid this down on his screen :

Quote:

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.

Or try interleaving the pages of two books. They push in fairly easy,
but you try parting them again by pulling.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

#23

On Tue, 10 Nov 2009 20:41:33 +0000, Harry Bloomfield wrote:

Quote:

Chris Whelan expressed precisely :
On Tue, 10 Nov 2009 18:06:00 +0000, 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.

By what process would a wheel bolt, tightened to the correct torque,
become significantly less tight?

Did I say significantly?

No, *you* didn't, but the OP said "nowhere near that tight".

Quote:

Check your cars handbook, most do recommend that the torque is rechecked
after a few miles.

Not any I've seen in the last twenty years or so.

Quote:

All/most car manuals also recommended that cylinder
head bolts are retorqued after 500/1000 miles it's all the same process
of settling in. The slightly high spots between the faces settle in and
the tightness declines.

Hang on! I'm having a "Life on Mars" moment!

Re-torquing head bolts went out with OHV engines, if not before.

Chris

--
Remove prejudice to reply.

#24

On Tue, 10 Nov 2009 21:21:56 -0000, Chris Whelan
<cawhelan (AT) prejudicentlworld (DOT) com> wrote:

Quote:

On Tue, 10 Nov 2009 20:41:33 +0000, Harry Bloomfield wrote:

Chris Whelan expressed precisely :
On Tue, 10 Nov 2009 18:06:00 +0000, 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.

By what process would a wheel bolt, tightened to the correct torque,
become significantly less tight?

Did I say significantly?

No, *you* didn't, but the OP said "nowhere near that tight".

Check your cars handbook, most do recommend that the torque is rechecked
after a few miles.

Not any I've seen in the last twenty years or so.

All/most car manuals also recommended that cylinder
head bolts are retorqued after 500/1000 miles it's all the same process
of settling in. The slightly high spots between the faces settle in and
the tightness declines.

Hang on! I'm having a "Life on Mars" moment!

Re-torquing head bolts went out with OHV engines, if not before.

Chris

Most engines still have overhead valves:-) But not many need re-torquing
nowadays.

#25

On Tue, 10 Nov 2009 21:36:32 +0000, Duncan Wood wrote:

[Missing tags added]

<Pedant>

Quote:

Most engines still have overhead valves:-) But not many need re-torquing
nowadays.

</>

:-)

Chris

--
Remove prejudice to reply.

#26

Paul wrote:

Quote:

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.

#27

Harry Bloomfield wrote:

Quote:

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!

:-)

#28

Charles C wrote:

Quote:

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?

#29

On Tue, 10 Nov 2009 21:43:11 -0000, Mrcheerful <nbkm57 (AT) hotmail (DOT) co.uk>
wrote:

Quote:

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.

#30

Mrcheerful wrote:

Quote:

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