I just remembered why I hated school. Thanks for the memories.

Because no one came forward to help you I will explain it to
you myself. Could be helpful when "educating college
engineering students."

A quantity consists of a value (also called magnitude) and a
unit (also called dimension), for example "4 quarts," or "1
gallon." Here, "4" and "1" are the values and "quarts" and
"gallon" are the units of the quantities. In these examples
the values and the units are different, but they both specify
the same quantity because 4 quarts equal 1 gallon. So, it is
irrelevant in what units a quantity is expressed, but it is
common to choose units that yield easy to handle values -
avoiding very small or very large numbers.

And if you are specific about the "other assertions" I will
help you with those, too.

Now, would you please help me? I don't understand your first
paragraph. But this could be because I am neither a mechanic
nor am I a metallurgist, and I didn't have the benefits of
"materials 101." When rewriting it, please pay particular
attention to the implications of, "the cut of the threads does
not tend to tighten the bolt,"  and, "The threads are helically
cut on both coarse and fine thread designs, of course, so
back-and-forth vibrating forces will tend to have the same
effect on both." What would be the effects if the threads were
not helically cut, and what bolts would these be?

If someone else would like to address this gentleman's comment above and his
other assertions, then please be my guest.

snip for brevity

snip

The units are irrelevant as long as the quantities
are correct.

Normal operating conditions or not, a moment of force
is commonly called torque.

Whatever that is, it is beyond me to see any relevancy
to the bolt tightening debate.

What would this be good for - the bolt should remain
lose "upon commencing operations"?

It's not the greater surface area that "holds fine
threaded applications more tightly together," it is
the smaller lead (the pitch in a simple bolt).
<http://www.efunda.com/designstandards/screws/faste
ners_intro.cfm?search_string=thread>

Galling is abrasion and fusion caused by friction,
not heat cycling.

I agree with Jim that, upon vibration, the cut of the threads does not tend
to tighten the bolt. Your Figure 3, Burt, doesn't show anything different
from a coarse thread cut. The threads are helically cut on both coarse and
fine thread designs, of course, so back-and-forth vibrating forces will tend
to have the same effect on both, absent other forces being at work.

So far I think the rest of the site has much to offer.

I would suggest

1.
Making sure you use the right units for torque. The units for torque in
automobile manuals are conventionally given as ft-lbs or newton-meters in
manuals. I realize English is not your first language, so maybe something
got lost in translation here.

2.
From my reading, "momentum force" is not a commonly accepted way of
characterizing the forces acting on the pulley under normal car operating
conditions. Inertial force is okay, being one way of saying centrifugal
forces are what mostly tend to push it off the crankshaft. (Recognizing, for
the physics-inclined among us, that whether it's accurate to call the
effects of centripetal forces "centrifugal forces" depends on what frame of
reference is used. What "centrifugal force" means in practical, hands-on
applications is well-understood, so I'm using it.)

3.
Your wording is not perfect, but then rarely is mine. I can understand your
other points and tend to agree with them. I think it is particularly
noteworthy that oil is supposed to be used, /not/ something like Loc-Tite,
on the threads. For now, I agree the purpose is to ensure that the bolt and
shaft threads can move relative to each other upon commencing operations.

4.
I want to look further into your hypothesis about what causes that loud
crack when the bolt frees. I think you're right that it may be due to
release of a large axial load in the bolt and so is a sonic boom(?). If it
is a sonic boom, then that does tend to suggest that the pulley bolt is in
fact under very high axial load. It's not, like Tegger has been contending,
merely the galling of female and male threads against each other,
essentially adhering one to the other.

5.
OTOH, I think galling does play a role. One need only consider some of the
exhaust bolts that become so hard to remove. Many of them are fine threaded
(not sure if they're super-fine, non-standard fine threads or not). Fine
threads are used to minimize the likelihood of the bolts vibrating free
during operation. The greater surface area contact between male and female
threads is what holds fine threaded applications more tightly together than
coarse threads. But unlike the pulley bolt, the exhaust bolts don't have a
rotating mass attached to them. The exhaust bolts also get very hot, though,
and they also vibrate while they're hot. Heat cycling--temperatures being
alternately raised and lowered, causing the metal to expand and contract and
fill in whatever microscopic gaps there are between male and female thread
surfaces--may play a huge role, as I believe SoCalMike, for one, proposed.
So the exhaust bolts seize up principally due to galling. (Not sure they're
all so terribly exposed to, say, gases of combustion causing corrosion,
though. Temperature may cause foreign materials on the bolt to crud up the
thread surfaces, OTOH.) The exhaust bolts are all I believe notably smaller
in diameter than the pulley bolt. Is the torque required to loosen these
exhaust system bolts in some proportion to the pulley bolt torque? I
couldn't say with certainty. In sum, right now I personally can't rule out
either a highly axially loaded bolt or galling due to massive heat cycling
causing that loud "crack" when one frees the pulley bolt.

6.
At the bottom of your site, I do not think your explanation of why the
loosening torque is often higher than the tightening torque is accurate. I
agree with boltscience.com , Tegger, and Scott that the main reason the
loosening torque is higher is the difference between the dynamic coefficient
of friction and the static coefficient of friction. The static coefficient
is higher.

Jim, re your current investigation: All you noted is interesting. For me,
the fretting on the one car's bolt-washer mating surfaces is particularly
so.

I would hypothesize that the 92 vehicle hadn't been in operation long with
the loc-tited bolt. Also, if it had continued to run for some time, it was
at higher risk of the pulley bolt coming undone, since no oil was used to
facilitate relative (tightening) motion between female and male threads,
leaving the vibrations/pulsing of the pulley against the bolt head to
potentially overwhelm the system, vibrate free the bolt, and so knock the
pulley free of the crankshaft.

I hope you bring "pillows" to the yard when you're jumping up and down on
that 1.5 foot breaker bar.   ;-)

I may take pictures in a few weeks if I free up my Civic's pulley bolt
during a tire rotation, and the safety engineers among us can have at it.

This remains an interesting academic debate, for bona fide engine
enthusiasts (pity the poor soul who comes here lately just wanting to know
whether he should change the washer for his oil drain plug at every oil
change!). I trust others here are wise enough to keep the boxing gloves off
and attend to them. I for one put my web site back up, and it does have some
changes reflecting some of the discussion here, FWIW.

Elle
Still an amateur learning much from those with specialized experience!

that's bunk.  you're citing rolled vs. cut threads as evidence of some
kind of ratchet mechanism?  no.  threads are rolled for fatigue
resistance - rolling has nothing to do with ratcheting.  oh, and yes, i
/have/ looked at plenty of bolts under microscopes, thanks.

As I suspected. I've created a page just to explain my reasoning
check it out here.

http://square.cjb.cc/bolts.htm

this afternoon, i went to my favorite junkyard and bought two crank
bolts.  one from an 91 civic, one from a 92 civic.  i'm going to post
the pics later this evening, but the observations are these:

_91_
* eyeball=poppingly hard to shift - had to get a fulcrum and bounce full
bodyweight at the end of a 18"x3/4" breaker bar.
* no evidence of loctite.
* clear fretting damage on the mating surface between the washer & the
bolt head.
* no evidence of corrosion.  [i'm in california]
* pulley wheel locked with single woodruff key.

_92_
* it was definitely snug, but i could remove with one hand.
* bolt thread clearly loctited.
* no evidence of fretting.
* no evidence of corrosion.
* pulley wheel splined /and/ woodruffed.

now, we all know what loctite does - it binds threads so they don't
move.  no movement means no possible further tightening.  loctite also
means a bolt is hard to remove compared to its fastening torque.

conclusions:

1. there is /definitely/ lash in the 91 pulley wheel - something that
honda evidently felt needed to be addressed with the addition of a
splined interface for the 92.  [splines don't eliminate lash, but help
mitigate it.]  fretting [or lack thereof in the case of the 92] is as
clear an evidence of lash as you can get.

2. loctite /prevents/ further tightening of the bolt!  hence the 92 was
much easier to remove, despite the loctite's binding function.  the
reduced lash would help in this regard also.

time to get out the camera...