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:
* 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
* no evidence of corrosion. [i'm in california]
* pulley wheel locked with single woodruff key.
* 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.
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...
Jim: Properly tightened, that bolt does NOT allow any sort of movement. It
/cannot/, and it /does not/. Period. Full stop. End of story.
You may be an electronics whiz, but you are clearly no mechanical engineer.
The pulley and the pulley bolt do NOT move in use, and the bolt absolutely
does NOT rotate so as to "tighten" after initial torque.
If you choose to believe that the bolt tightens more through rotation after
initial tightening torque, then you are misleading yourself and everyone
who reads your posts.
There are many reasons why some crank bolts are difficult to remove.
Rotation after initial tightening torque is *NOT* one of them.
Hmmm, not to add to the confusion, but...
I don't know how much relevance this has to crankshaft pulley bolts, but
on every table saw or radial-arm saw I've ever used, reverse-threaded
nuts are used to hold the blade on the threaded shaft, because the
clockwise (looking at the shaft) rotation of the blade would cause a nut
with a normal thread to come loose and spin off. And yes, they do
tighten up, with very little use.
Same thing on my angle grinder, my right hand and left hand radial arm
saw. The bolt/nut are screwed in the opposite direction of the spinning
blade. Even finger tight the bolt/nut will tighten (spin inward) over time.
This is caused by (my theory) the force of acelleration of the motor is
stronger than the inertial mass of the blade. Another words, the blade
wants to sit still. Now, if you look at the face or washer of the bolt you
realize that it has a greater surface area contact than on the other side
of the blade. The greater surface area (should not be oil or otherwise
the bolt won't tighten) is actually moving. However, the threads should
be oiled to prevent galling. I believe the same principle is used on the
Totally different application.
Honda is just about the only manufacturer whose bolts run in a tightening
direction. Everybody else has bolts that run in a LOOSENING direction, and
these DO NOT COME LOOSE IN USE.
Everybody elses' bolts are the same as Honda's, and are torqued to similar
That's one difference. Also the automotive pulley bolts are to be torqued
to such a figuure as to prevent movement. Your saw blade nuts/bolts are
just snugged by hand to an unknown torque, and are meant to be repeatedly
removed and replaced.
"Honda is just about the only manufacturer whose bolts run in a tightening
direction. Everybody else has bolts that run in a LOOSENING direction, and
these DO NOT COME LOOSE IN USE." Nobody can explain why this is, if it's
assumed that the pulley and bolt can move relative to the crank.
And even on a Honda, a pulley bolt insufficiently tightened (as little as
20 lbs short of the proper figure), will eventually result in a bolt that
*FALLS OUT*. Talk to any mechanic familiar with this subject.
The damned assembly is SOLID in use when properly assembled. Nothing
anybody says here will change that fundamental fact.
Spines can reduce or eliminate movement if the spines channels are
tapered. This is noticeable when you will require a gear puller to remove
the pulley. But woodruff key aren't and they can produce play, or
movements. I once removed a crank bolt (1988 at 180k miles) with a key.
The face of the bolt is pretty worn from movements. Unlike a radial-arm saw
the inertia from the weight load on the pulley develops in both directions but
the bolt has to move in one direction so the woodruff key is used.
What do you mean?... Honda have made motors than spin clockwise and
counterclockwise. And the crank bolts are always Lefty Lucey and Righty Tighty.
i've just emailed you the photo evidence. if you host it, we can all
i'm no electronics guy and no engineer. i'm an [ex] metallurgist. and
metallurgists spend a big proportion of their time sorting out the
screw-ups the engineers make because half of them don't know what
they're doing and were asleep in materials 101 or are too egotistical to
bother to ask.
check your email. i've just sent you the galling evidence. it's a
perfect textbook example.
the loctited bolt/splined pulley does not move. the torque-only
bolt/woodruff-only pulley does. the galling proves it.
except that we have the photo evidence to prove to the contrary!
The pics are here:
Unfortunately, the pics aren't really evidence of much other than this:
You've taken photos of a pulley from an unknown car with an unknown history
given unknown servcicing by persons of unknown competence.
These pics are strongly suggestive of a pulley having been installed at
some point with no Woodruff key, or otherwise installed incorrectly. I can
assure you a pulley properly installed will not gall that way.
A properly tightened joint dowes not rotate. Your pictures do not prove
anythng one way or the other because we do not know the car's history.
on the one hand, it's healthy to be skeptical. on the other, i've done
enough failure analysis on enough machinery to know what i'm looking at.
i can also deduce something of the service history based in what i see.
sorry, but i'm the guy that took it off. and if you can't accept that
the pictured galling happened with the key installed, then we have a
debate beyond the tech arena. the woodruff key, the pulley wheel and
the crank keyway were all in perfectly acceptable condition, although
there was evidence of lash - much like the lash evident on the splines
of a driveshaft. there was no evidence of the pulley wheel ever having
been spun out.
without the woodruff, the pulley would absolutely rotate. the more the
bolt was torqued, the more difficult it would be to turn, but saying it
won't & can't move is like denial of elasticity.
regarding the 91 vehicle's history, i know that it had been relatively
well serviced. it had 220k miles. and that pulley bolt had been
removed 3 times. you can't see it from the pic, but the skid mark at 2
o/c on the l/h bolt's washer in this pic:
it has 3 of those skidmarks, coinciding with the keyway, one for each
removal. the galling evident on the other side of the washer is not
what you would see from 3 removals. not by any stretch.
the 92 bolt otoh, you can see the evidence of one removal [evident from
the keyway mark] on the bolt, by me. the bolt side of that washer shows
some minor skid evidence, but as you can see, it's not impacted the
plating and there's no evidence of galling whatsoever.
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.
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
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.
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.)
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.
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.
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.
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
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
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.
Still an amateur learning much from those with specialized experience!
wrote> > that's bunk. you're citing rolled vs. cut threads as evidence of some
Jim, I don't cite rolled vs. cut threads as evidence of some kind of
ratchet mechanism, the images were simply not well drawn. I was
citing the mechanisms that cause the bolt to wind inwards caused by
they way the bore is tapped and the effects of the pulley.
Galling is possible on the exhaust bolt since they don't require lubricants.
Once locked together you will notice the extreme "snap" upon release. O2
sensor are one the parts that can benefit from the anti-seize compound to
prevent galling. On some areas on the exhaust system, self locking nuts
are used instead.
Good work for showing what I should fix. I probably have to add better
sketches to visualize a theory and avoid further confusions. Several
sections are fixed based on your input and others not pertaining to the
crank bolt is eliminated.
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