anti-seize and torque settings

"Carlo Vittoli" <vittoli@gmail.com> wrote in message
news:m3y7c9t9j5.fsf@uranio2.dev.tiscali.its...

> a physicist who worked in the FIAT research center, discussing the use
> of antiseize compound, said that the torque is basically given by
> friction between bolt head and mating surface, not friction between
> threads. This is convincing, because you start finding a meaningful
> resistance, when you install a bolt, only when the bolt head touches
> the surface. So, basically, unless you apply antiseize/lubricant to
> bolt head, torque reading should be essentially the same

Um, could it be that until the bolt head contacts and puts load on the
threads, there will be no meaninful resistance from the threads? I'm not
discounting the effect of the bolt head. Most of my honda manual state that
head and cylinder bolts should have the threads and bolt head lubricated.
I believe that specs for lubricated bolts will give much more consistent
results.

-Jeff-

> a physicist who worked in the FIAT research center, discussing the use
> of antiseize compound, said that the torque is basically given by
> friction between bolt head and mating surface, not friction between
> threads. This is convincing, because you start finding a meaningful
> resistance, when you install a bolt, only when the bolt head touches
> the surface. So, basically, unless you apply antiseize/lubricant to
> bolt head, torque reading should be essentially the same

Ah, physicists...those guys crack me up.

The force in lbs. at the surface/head junction will be exactly
equivalent to the force on the threads. I would further expect that a
typical surface area entire mated thread length to exceed that of the
surface/head junction. As such, I would expect the effect of friction
on the mating surface to be small.

JayC

"Jeff Deeney" <jld@nospam.com> writes:
> Um, could it be that until the bolt head contacts and puts load on the
> threads, there will be no meaninful resistance from the threads?

this sounds very reasonable. On the other hand, looking at the torque
formula on page 17 in the pdf file linled by sturd (or on
http://euler9.tripod.com/fasteners/preload.html), the contribution of
bolt head is 0.625*friction_coeff, which, using coefficents from table
on page 16, looks quite high. Even too high, considering that typical
values should be around .2, so probably the choice of the proper value
for the friction coefficient is not trivial.

I'm confused. If I had a torque wrench, I would try measuring the
torque for a clean bolt, a thread-greased bolt, a head-greased bolt,
and a totally greased bolt, and compare the values. Theory will then
be adapted to experimental results :-)

--
Carlo Vittoli
Quartu S.Elena, Sardinia, Italy

Carlo Vittoli is truly confused:

> I'm confused. If I had a torque wrench, I would try measuring the
> torque for a clean bolt, a thread-greased bolt, a head-greased bolt,
> and a totally greased bolt, and compare the values.

And you'd get the exact same torque unless you also had
an extensometer.


Go fast. Take chances.
Mike S.

"JayC" <jwc@sysmatrix.net> wrote in message
news:0dba5d95-ea29-4a9d-8591-f2453355a02c@s19g2000prg.googlegroups.com...

> The force in lbs. at the surface/head junction will be exactly
> equivalent to the force on the threads. I would further expect that a
> typical surface area entire mated thread length to exceed that of the
> surface/head junction. As such, I would expect the effect of friction
> on the mating surface to be small.

In theory, frictional force in independent of area.

-Jeff-

> In theory, frictional force in independent of area.
>
> -Jeff-

Doesn't that belong in the skinny tires and VW in the snow thread?

On Wed, 05 Dec 2007 08:02:06 -0800, Carlo Vittoli <vittoli@gmail.com>
wrote:

> "Whelan - '02 200exc (x2) & '04 MTD 38" <yosef@sisna.com> writes:
>> "Use an antiseize compound on all cylinder head studs to get a more
>> accurate torque reading."
>>
>> Didn't we conclude torque specs are based on solvent-cleaned threads
>> and using antiseize then torquing over-torques?
>
> a physicist who worked in the FIAT research center, discussing the use
> of antiseize compound, said that the torque is basically given by
> friction between bolt head and mating surface, not friction between
> threads. This is convincing, because you start finding a meaningful
> resistance, when you install a bolt, only when the bolt head touches
> the surface. So, basically, unless you apply antiseize/lubricant to
> bolt head, torque reading should be essentially the same
>
> Ciao



--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

Carlo,

I once owned a Fiat 850 Spyder, 1967 year. It snapped rear motormounts if
you looked at it crosswise. I don't think Fiat is a font (bastion?) of
reliability and quality, especially with things mechanical. Although
Mazda, through Ford sponsorship is trying to win the "parts all over the
road" crown.

Bono fortuna,

Joe

On Dec 5, 3:17 pm, "Joseph Rooney" <ikeroone...@yahoo.com> wrote:

> I once owned a Fiat 850 Spyder, 1967 year. It snapped rear motormounts if
> you looked at it crosswise. I don't think Fiat is a font (bastion?) of
> reliability and quality, especially with things mechanical. Although
> Mazda, through Ford sponsorship is trying to win the "parts all over the
> road" crown.

I had one of those. First car I ever owned. A true classic piece of
shit. I bought mine around '72 or '73. If it was yours previously,
thanks a pile!

"Dean H." <moto@groove.calm> wrote in message
news:h56dnXkmkbnYYsvanZ2dnUVZ_h6hnZ2d@comcast.com. ..
>
>> In theory, frictional force is independent of area.
>>
>> -Jeff-
>
> Doesn't that belong in the skinny tires and VW in the snow thread?

When you start working with compliant materials (like rubber/sand/snow) with
multiple gripping edges (tire treads) the equation changes.

I always use anti-sieze or oil on hi-torque engine bolts. Being "at one"
with the metal, torque wrenches are only an approximate guide to my art. I
will go to the click, then until it "feels right". If continued clockwise
rotation results in decreasing torque, I simply back up to the point where
the threads are once again firm.

-Jeff-

On Dec 5, 2:02 pm, sturd <mikesturdevant...@hotmail.com> wrote:
> Carlo Vittoli is truly confused:
>
> > I'm confused. If I had a torque wrench, I would try measuring the
> > torque for a clean bolt, a thread-greased bolt, a head-greased bolt,
> > and a totally greased bolt, and compare the values.
>
> And you'd get the exact same torque unless you also had
> an extensometer.
>
> Go fast. Take chances.
> Mike S.


Amend that to "torque to the same torque and count turns" and it'll
get you there.


DDave