Page 9 of 12
valve adjustment
Posted: Sat Aug 06, 2005 2:20 pm
by Eric L. Green
On Sat, 6 Aug 2005, Ed Chait wrote:
>> To make it go as smoothly as possible, make sure you have a shim pack
>> from Fred and a 1/4" torque wrench with a long extension bar so that
>
> Doesn't using an extension on a torque wrench change the leverage and affect
> the value you are torquing to?
Nope. Not unless it has an offset in it. Torque consists of force applied
over a distance. The distance in this case is the distance between where
the force is being applied (i.e. at the bolt) and a 90 degree line through
the end of the torque wrench handle. As long as this distance doesn't
change, the torque applied with a given input to the handle doesn't
change. Thus as you can see, simply adding an extension (without putting a
u-joint or some other such thing into the equation) doesn't change the
torque applied with a given input to the handle... it just moves the point
where the force lines intersect downwards a bit.
-E
valve adjustment
Posted: Sat Aug 06, 2005 11:59 pm
by Ed Chait
> On Sat, 6 Aug 2005, Ed Chait wrote:
>>> To make it go as smoothly as possible, make sure you have a shim pack
>>> from Fred and a 1/4" torque wrench with a long extension bar so that
>>
>> Doesn't using an extension on a torque wrench change the leverage and
>> affect
>> the value you are torquing to?
>
> Nope. Not unless it has an offset in it. Torque consists of force applied
> over a distance. The distance in this case is the distance between where
> the force is being applied (i.e. at the bolt) and a 90 degree line through
> the end of the torque wrench handle. As long as this distance doesn't
> change, the torque applied with a given input to the handle doesn't
> change. Thus as you can see, simply adding an extension (without putting a
> u-joint or some other such thing into the equation) doesn't change the
> torque applied with a given input to the handle... it just moves the point
> where the force lines intersect downwards a bit.
>
> -E
Of course, that makes sense.
For some reason, I had the mental image of an extension applied to the
handle of the torque wrench and a 90 degree angle.
D'oh!!!!!
ed, just call me homer
A17
valve adjustment
Posted: Sun Aug 07, 2005 8:19 am
by Rick McCauley
I took mechanical training under 3 instructors. All 3 taught that an exstension will alter actual torque getting to the bolt. I could never understand it, but that's what they taught.
Rick A17
>
> Nope. Not unless it has an offset in it. Torque consists of force applied
> over a distance. The distance in this case is the distance between where
> the force is being applied (i.e. at the bolt) and a 90 degree line through
> the end of the torque wrench handle. As long as this distance doesn't
> change, the torque applied with a given input to the handle doesn't
> change. Thus as you can see, simply adding an extension (without putting a
> u-joint or some other such thing into the equation) doesn't change the
> torque applied with a given input to the handle... it just moves the point
> where the force lines intersect downwards a bit.
>
> -E
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valve adjustment
Posted: Sun Aug 07, 2005 10:20 am
by Doug Herr
On Sun, 7 Aug 2005, Rick McCauley wrote:
> I took mechanical training under 3 instructors. All 3 taught
> that an exstension will alter actual torque getting to the
> bolt. I could never understand it, but that's what they taught.
Maybe the torsional energy delivered to the extension is not
fully passed on to the nut/bolt. Seems like it would be a
minimal issue tho.
--
Doug Herr
doug@...
valve adjustment
Posted: Sun Aug 07, 2005 11:47 am
by Eric L. Green
On Sun, 7 Aug 2005, Rick McCauley wrote:
> I took mechanical training under 3 instructors. All 3 taught that an
> exstension will alter actual torque getting to the bolt. I could never
> understand it, but that's what they taught.
I'm sorry that my description of the physics involved is so pathetically
inadequate (it really worked better back when I was teaching this stuff
when I could draw a picture on the chalkboard and then show some
physical examples), but anyhow, physics says differently.
Consider the whole notion of a "foot-pound". Let's say you're torquing a
bolt to 25 foot-pounds. That means that if you have a 1-foot-long wrench
from the center of the socket to the end, parallel to the ground, and hang
a 25 pound weight from the other end of the wrench, you're applying 25
foot-pounds of torque to the bolt. Now, let's put an extension between the
socket and the wrench. The distance from where the weight attaches to the
wrench and a line drawn through the center of the socket is *still* 1
foot. So you're *still* applying 25 foot-pounds of torque to the bolt.
Torque is force applied over a distance. That is how it is defined in
physics. Force is the same (25 pounds), distance is the same (one foot),
thus torque is the same, by definition.
What may have confused your instructors is the notion of an offset
extension, i.e., one which actually makes the distance from the end of the
wrench to the center of the bolt longer or shorter. This will affect the
amount of torque that a given force at the end of the wrench is applying
to the bolt, since you just changed the distance part of the above
equation. Also, if you hold the extension to stabilize it this obviously
changes things since you are now applying a force other than to the end of
the wrench. Other than that, the effect of an extension is minimal (since
it's unlikely that the extension is *exactly* vertical it may change the
distance by a tiny bit, but probably not by enough to be noticable
within the precision of the torque wrench).
-E
valve adjustment
Posted: Sun Aug 07, 2005 12:12 pm
by Rick McCauley
I just thought of something that backs up the idea that an extension makes a difference. My Uncle is a mechanic by trade, and has been for just under 40 years. He has a set of wheel lug extensions that vary in diameter and length. You choose the extension based on lug bolt diameter, rim, material etc. The same air gun is used, but no matter how much air pressure is put to the gun, the lugs get the correct amount of torque. I can't remember for sure but I think they are available through MAC or Snap-On. I wouldn't even try to figure out how they work, but if somebody knows of a MAC or Snap-On Rep, maybe it would be interesting to ask.
Rick A17
Doug Herr wrote:
On Sun, 7 Aug 2005, Rick McCauley wrote:
> I took mechanical training under 3 instructors. All 3 taught
> that an exstension will alter actual torque getting to the
> bolt. I could never understand it, but that's what they taught.
Maybe the torsional energy delivered to the extension is not
fully passed on to the nut/bolt. Seems like it would be a
minimal issue tho.
--
Doug Herr
doug@...
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valve adjustment
Posted: Sun Aug 07, 2005 4:55 pm
by scott quillen
I spent 9 years of my 20 in the Air Force wrenching on
Minuteman ICBMs. The Air Force is pretty picky about
nuclear surety and how its Minutemen are maintained
and we were trained to use sockets, crows feet and
extensions with our torque wrenches. The particular
things we were taught about torque wrench use:
1. Always store a torque wrench at its lowest setting.
2. Always "exercise" a torque wrench at its lowest
setting before use by clicking it at least 4 times in
each direction.
3. Never drop a torque wrench...if it happens, don't
use it again until it's been recalibrated by the PMEL
(Precision Measurement Equipment Laboratory).
4. The lowest 20% of a torque wrench's range is the
least accurate - always choose a torque wrench with
sufficient range to avoid using this lowest 20%.
5. Always apply torque is a slow, smooth motion until
the proper torque is achieved - AVOID JERKING the
torque wrench when applying torque as it is easy to
over-torque the fastener when jerking.
6. The fastener should be turned at least 1/4 turn
before the desired torque is achieved, to ensure the
fastener is not over-torqued. In other words, if the
wrench clicks as soon as it is turned, chances are
good the fastener is over-torqued.
7. NEVER used a cheater bar or extend the length of a
torque wrench - THIS will affect the applied torque.
8. Torque wrench accuracy can be affected by
temperature extremes. Always store torque wrenches at
"room temperature" prior to use. In Montana, we often
worked in temps WAY below zero, so we stored our
torque wrenches in a heated maintenance vehicle or in
the "soft support building" or in the LER (lower
equipment room)prior to use.
I think that about covers it.
Scott
--- Rick McCauley wrote:
> I took mechanical training under 3 instructors. All
> 3 taught that an exstension will alter actual torque
> getting to the bolt. I could never understand it,
> but that's what they taught.
>
> Rick A17
>
>
> >
> > Nope. Not unless it has an offset in it. Torque
> consists of force applied
> > over a distance. The distance in this case is the
> distance between where
> > the force is being applied (i.e. at the bolt) and
> a 90 degree line through
> > the end of the torque wrench handle. As long as
> this distance doesn't
> > change, the torque applied with a given input to
> the handle doesn't
> > change. Thus as you can see, simply adding an
> extension (without putting a
> > u-joint or some other such thing into the
> equation) doesn't change the
> > torque applied with a given input to the handle...
> it just moves the point
> > where the force lines intersect downwards a bit.
> >
> > -E
>
>
>
>
> ---------------------------------
> Start your day with Yahoo! - make it your home page
>
>
> [Non-text portions of this message have been
> removed]
>
>
>
> Archive Quicksearch at:
>
http://www.angelfire.com/ut/moab/klr650_data_search.html
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valve adjustment
Posted: Sun Aug 07, 2005 9:26 pm
by fasteddiecopeman
ONLY if the force is LATERALLY applied (a longer sideways force...).
Ed
> Doesn't using an extension on a torque wrench change the leverage and
affect
> the value you are torquing to?
>
> I really don't know, so I better ask before I do my first valve adjustment.
>
> ed
> A17
valve adjustment
Posted: Sun Aug 07, 2005 9:54 pm
by April Neave & Norm Keller
Someone posted:
>I took mechanical training under 3 instructors. >All 3 taught that an
exstension will alter actual >torque getting to the bolt. I could never
>understand it, but that's what they taught.
I seldom break my rule to not pronounce directly on a point of view but in
this case will do so.
Your instructors were wrong.
As long as the torque is axial there will be no reduction regardless of the
length of extensions.
If the torque is applied non-axially (that is to say, out of line) the
torque will be altered.
This is why it is quite acceptable to step out, down and back into line
again to go around an interference and still not alter torque. Offset
extensions are in common use for many applications.
It is important to recognize that torque is the measure of twisting effort
applied between two points. In other words, there must be an originator and
receiver for the torque to be discussed.
Speed needs have no effort applied and torque needs have no movement.
Movement and torque taken together are power.
If you search the archives much has been written with regards tightening of
fasteners. One point which should be clearly understood by anyone doing
service work is that the purpose of torquing a fastener is to create the
specified degree of tension in the fastener. The tension will result in the
desired stretch of the fastener and the desired clamping force will be
applied to the parts in question.
Torque tightening is a relatively inexact, and so inefficient, method of
arriving at the desired tensioning of the fastener.
A much more efficient method is the "torque turn" method used around large
equipment for more than 60 years to my knowledge. This same technique has
appeared in the automotive industry as "torque to yield" . Both names refer
to a method in which the fastener is snugged up and then turned a specified
number of degrees in order to reach the desired tensioning of the fastener.
If a fastener is to be tightened by turning a specified number of degrees,
the designer must decide how much tension and/or clamping force is needed to
be provided by the fastener. The amount of tension is easy to arrive at
since it is simply the amount of pull required to remove all the slack from
the assembly and then to proceed to stretch the fastener by a determined
amount. The determined amount can be calculated from the thread pitch and
the compression of the threads under the resulting load. Turn a given bolt
or screw tight, and then turn a specified number of degrees and a certain
tension will be achieved. Simple!
To achieve the same precision of tensioning through torque is much more
difficult. The same intent is there which is to achieve the same number of
degrees of turn but the method makes this much more difficult to achieve.
In order for the specified number of degrees of turn to be achieved, the
effort to turn the fastener must be predicted. Since this effort must both
apply tension through the screw thread pitch (easy to calculate) and
overcome friction (very difficult to predict) the method must be less
accurate than that which addresses the problem directly by simply turning a
determined number of degrees.
FWIW, now back to getting over vacation and back to business in the
morning.... (VBG)
Norm
valve adjustment
Posted: Sun Aug 07, 2005 9:54 pm
by April Neave & Norm Keller
>MAC or Snap-On Rep, maybe it would be interesting to ask.
The extension in question is usually referred to as a "torque stick" or the
like name. Accutorq were the first to market but several others have picked
up the same principle. The idea is that the extension has a certain
resistance to being twisted and so will transmit up to a certain amount of
twisting force (torque) before the extension begins to twist. After the
threshold torque (twisting force) has been applied the extension will wind
up and so will require much more rotation of the driving end in order to
continue to increase the twisting force.
If one were to put a hand wrench onto one end the extension will wind up and
then continue to apply torque increasingly until the extension fails. Any
increase in torque much above the designed torque requires quite a lot of
rotation due to the "give" and winding up of the extension.
When using an impact gun (air wrench) the torque bar will "soak up" the
impacts of the wrench and so tend to limit the applied torque to that
specified. This works well as long as an impact gun with too much power is
not used. For this reason the makers provide a procedure to ensure that one
doesn't over power the extension.
Torsion bars are commonly used as suspension springs in many automotive and
light truck applications. The first Honda 450 motorcycle was a wonder of
design due to its torsion bar valve springs.
Now I really had better get to the chores (LOL)
Norm