Cranks on Axles - to grease or not?
Mike Ellwood
(which is _not_ my intention)
what are people's feelings about greasing axles
before fitting a crank?
I have heard arguments for and against.
In any case, do people think it'sa good idea to regularly
remove them, to avoid "bonding" occuring?
TIA,
Mike Ellwood Mike.E...@rl.ac.uk
speaking for himself, and not for:
CCL Rutherford Appleton Laboratory
Chilton, DIDCOT, Oxon
GB OX110QX
Tel: 01235-446161 Fax:01235-446626
Kenneth Cline
|> At the risk of starting a controversy
|> (which is _not_ my intention)
|> what are people's feelings about greasing axles
|> before fitting a crank?
From the FAQ (Rec.Bicycles_Frequently_Asked_Questions_Posting__Part_4_5):
Subject: 8.45 Installing Cranks
From: Jobst Brandt <jbr...@hpl.hp.com>
...
The admonition to not lubricate the tapers of the crank spindle seems
to find life only in bicycle cranks among all the machines I have ever
seen. I have never heard a mechanical or metallurgical explanation
for this "dry assembly" instruction. If it is metal to metal galling
to which the adherents of this method aspire, they should prescribe a
suitable degreaser to assure that it will occur. Manual contact
(finger prints) alone, generally imparts enough grease to constitute
lubrication while specifically applying a lubricant guarantees that a
known kind and quantity of, rather than accidental grease is present.
Regardless, whether grease or no grease is used, in use, the spindle
and crank will make metal to metal contact and cause fretting
corrosion for all but the lightest riders. The purpose of the
lubricant is to give a predictable press fit for a known torque. If
the spindle is completely dry this cannot be said and for other
conditions, some galling may occur on installation. Lubrication is
only used to guarantee a proper press without galling because it is
displaced in use. That taper faces show erosion and rouge after
substantial use proves that the lubricant was displaced.
Only the press fit, not friction, transmits loads from crank to
spindle. As any bicycle mechanic can tell you, crank bolts are often
'nearly loose' after use and the left one more so than the right.
This occurs because the left end of the spindle experiences torque and
bending simultaneously while the right end gets them one at a time.
The right pedal does not put any significant torque into the spindle.
Either way, the looseness occurs because loads make the crank squirm
on the spindle and the only direction it can move is up the taper.
The retaining bolt blocks the other direction.
"Dust caps" aren't just dust caps but retention for loose bolts. It
is not that the bolt unscrews but that the crank moves up the taper.
However, once the screw is unloaded it can subsequently unscrew and
fall out if there is no cap.
The NO GREASE admonition is an old wive's tale that must have
propagated up from some bike shop. It makes no sense whatsoever. I
have yet to see a logical explanation other than so and so said so. I
believe that some bike shops are concerned that they might strip out
retaining bolts as was the problem with low quality Campagnolo cranks.
In that effort they advised to re-tighten the screws after every ride
for a week. This spells disaster because for strong and heavy riders
this can split the crank right down the middle.
Because cranks squirm farther up the taper when stressed highly, the
unwitting mechanic believes the screw got loose, rather than that the
crank got on tighter. By pursuing the crank with its every move up
the spindle, an extremely high press fit results. I have seen cranks
that were split by this procedure. This may be is where the NO GREASE
fable was born.
Jobst Brandt <jbr...@hplabs.hp.com>
John Stone
(Kenneth Cline) wrote:
> In article <3ug1rj$2j...@unixfe.rl.ac.uk>, m...@unixfe.cc.rl.ac.uk (Mike
Ellwood) writes:
> |> At the risk of starting a controversy
> |> (which is _not_ my intention)
> |> what are people's feelings about greasing axles
> |> before fitting a crank?
-- Lots-0-stuff deleted--
> "Dust caps" aren't just dust caps but retention for loose bolts. It
> is not that the bolt unscrews but that the crank moves up the taper.
> However, once the screw is unloaded it can subsequently unscrew and
> fall out if there is no cap.
The bolts come loose because they used grease on the BB axle.
> The NO GREASE admonition is an old wive's tale that must have
> propagated up from some bike shop. It makes no sense whatsoever. I
> have yet to see a logical explanation other than so and so said so. I
> believe that some bike shops are concerned that they might strip out
> retaining bolts as was the problem with low quality Campagnolo cranks.
> In that effort they advised to re-tighten the screws after every ride
> for a week. This spells disaster because for strong and heavy riders
> this can split the crank right down the middle.
Actually you have this backwards, the crank goes on and then the bolt
bottoms out because the crank arm continues to move up the BB axle(farther
than it should). There by causing the crank arm to wallow out causing it
to become perpetually loose.
This comes from years of experience in the bike industry, not from an FAQ.
The only cranks we have had problems with are the ones that some other
shops have put grease on the BB axle, before putting on the crank axle.
Never, Never, Never put grease on the crank axle.
Hope this helps,
John Stone
ig...@gate.net
> Never, Never, Never put grease on the crank axle.
>
> Hope this helps,
>
> John Stone
>
>>>>
BALOGNA! Submit some proof that this actually does happen. I've tried it both ways and have found
the above to not be the case. ANY crank arm that has been properly tightened and left on the bike for
an extended period before removal (say a couple years) is going to be a bitch to remove. A thin layer
of grease on the tapers will keep any possible corrosion caused by the two dissimilar metals from
becoming a problem. It WILL NOT make the crank arm slide further up the spindle when tightened.
Crank arms are not made of play dough.
Jim
Kenneth Cline
|> In article <3ugdm1$o...@casaba.srv.cs.cmu.edu>, cli...@SILVER.FOX.CS.CMU.EDU
|> (Kenneth Cline) wrote:
|> > "Dust caps" aren't just dust caps but retention for loose bolts. It
|> > is not that the bolt unscrews but that the crank moves up the taper.
|> > However, once the screw is unloaded it can subsequently unscrew and
|> > fall out if there is no cap.
etc.
Please get the attribution correct! I did not write this paragraph (or the
others you have attributed to me). This material, which is an excerpt of
the rec.bicycles FAQ (section 8.45), was quoted, not written, by me.
Oh well... Your response dashed my hopes that a well written FAQ could
prevent needless discussion.
Ken
mbus...@icaen.uiowa.edu
|> In article <3ugdm1$o...@casaba.srv.cs.cmu.edu>, cli...@SILVER.FOX.CS.CMU.EDU
|> (Kenneth Cline) wrote:
|>
|> Ellwood) writes:
|> > |> At the risk of starting a controversy
|> > |> (which is _not_ my intention)
|> > |> what are people's feelings about greasing axles
|> > |> before fitting a crank?
|>
|> -- Lots-0-stuff deleted--
|>
|> > is not that the bolt unscrews but that the crank moves up the taper.
|> > However, once the screw is unloaded it can subsequently unscrew and
|> > fall out if there is no cap.
|>
Good cause and effect here :) Why? Its common practice
to put lube of some sort on any fastener you want to torque.
Not that the torque readings are correct, but they are better than
if you do it dry because you can get rid of a lot of slip-stick.
|> > The NO GREASE admonition is an old wive's tale that must have
|> > propagated up from some bike shop. It makes no sense whatsoever. I
|> > have yet to see a logical explanation other than so and so said so. I
|> > believe that some bike shops are concerned that they might strip out
|> > retaining bolts as was the problem with low quality Campagnolo cranks.
|> > In that effort they advised to re-tighten the screws after every ride
|> > for a week. This spells disaster because for strong and heavy riders
|> > this can split the crank right down the middle.
|>
|> Actually you have this backwards, the crank goes on and then the bolt
|> bottoms out because the crank arm continues to move up the BB axle(farther
|> than it should). There by causing the crank arm to wallow out causing it
|> to become perpetually loose.
This is WACK! A little grease isn't going to do jack as far as
enabling the crank arm to creep and work its way up the taper. From what
I have seen, this requires that the crank be severly plastically deformed.
We'talking cats and dogs living together... Its not just "sliding" along. If the
crank is moving farther and farther up the taper, its presumably getting
tighter and tighter. How can it wallow out? It can't unless it was
already damaged or something.
I think the problem comes from cranks which are damaged by not
adequately tightening them the very first time, which damages the taper.
I just cranked the hell out of mine the first time I put them on;
never have came loose in 5 years w/o dustcaps.
|> This comes from years of experience in the bike industry, not from an FAQ.
|> The only cranks we have had problems with are the ones that some other
|> shops have put grease on the BB axle, before putting on the crank axle.
Sorry, but my years of experience with the bike industry has left me
less than impressed with its years of experience.
|> Never, Never, Never put grease on the crank axle.
I'll believe it when I see good cause/effect reasoning....
If there is significant evidence otherwise, I would suspect something
else going on.
Matt>
Jeffrey Potoff
On Thu, 20 Jul 1995, John Stone wrote:
> This comes from years of experience in the bike industry, not from an FAQ.
> The only cranks we have had problems with are the ones that some other
> shops have put grease on the BB axle, before putting on the crank axle.
>
> Never, Never, Never put grease on the crank axle.
>
Then I suppose that you have problems with all mass produced bikes as
they all come assembled with grease on the BB axle. The crank is a press
fit on the BB axle, held in place by the crank bolt, how on earth would
grease on the BB axle allow the crank to move ?
Jeff
Joshua_Putnam
As it happens, before SR Suntour pulled out of the U.S. they had
tech support email, and I asked them about this very topic. They
referred my email to their engineers, who gave a response that
makes a little sense and also dispells most of the folklore about
greased tapers.
Greasing the taper allows the crank to press on a little further
when it is first installed. This screws up the chain line during
the intial setup of the drivetrain. Period. Their engineers
specifically stated that greasing the taper has no bearing on
crank wear, splitting the taper socket, etc., and that a greased
taper was a better idea in theory but, as is so often the case,
the standard was set years ago and that's that.
--
Jo...@WOLFE.net is Joshua Putnam / P.O. Box 13220 / Burton, WA 98013
"My other bike is a car."
Bike parts for sale: finger Joshua...@gonzo.wolfe.net for list.
William Kellagher
>The only cranks we have had problems with are the ones that some other
>shops have put grease on the BB axle, before putting on the crank axle.
>
>Never, Never, Never put grease on the crank axle.
>
>
>John Stone
Well, John, here's another data point for your years of experience in the bike
industry: I Always, Always, Always put grease on by bottom bracket spindle
tapers before I install a crank. I also Always, Always, Always replace the
dustcap over the crank bolt. I Never, Never, Never have a problem with my
cranks loosening. I've Never, Never, Never bottomed out a crank on the spindle.
And I've Never, Never, Never split a crank where it connects to the spindle.
At least not in the last 60,000 miles of riding, anyway, anyway, anyway.
Give me a break, Give me a break, Give me a break.
Bill Kellagher
Boulder, Co
Mike Iglesias
John Stone <jst...@iglou.com> wrote:
>This comes from years of experience in the bike industry, not from an FAQ.
>The only cranks we have had problems with are the ones that some other
>shops have put grease on the BB axle, before putting on the crank axle.
>
>Never, Never, Never put grease on the crank axle.
I've had my current road bike since mid-1988, roughly 10k miles. I've
always lightly greased the BB tapers, and I haven't had any problems with my
cranks. They haven't moved up the tapers, the bolts have not come loose,
etc.
Maybe all the ones you've seen that were screwed up had the bolts torqued
way too high, or they were ridden when they were loose on the BB, which
messed up the holes in the cranks?
--
Mike Iglesias Internet: igle...@draco.acs.uci.edu
University of California, Irvine phone: (714) 824-6926
Office of Academic Computing FAX: (714) 824-2069
Mike Ellwood
having read the FAQ *blush* - I will remedy this asap.
Mike.E...@rl.ac.uk
Jim Collias
|> ANY crank arm that has been properly tightened and left on the bike for
|> an extended period before removal (say a couple years) is going to be a
|> bitch to remove. A thin layer of grease on the tapers will keep any
|> possible corrosion caused by the two dissimilar metals from becoming a
|> problem. It WILL NOT make the crank arm slide further up the spindle
|> when tightened. Crank arms are not made of play dough.
|>
|> Jim
|>
A couple of years is a very long time between crank removals.
I've never greased the tapers on my BB axles and had no problems
of any kind with that interface. However, I have seen a few
inexperienced and BB mechanics grease everything down there, then
proceed to bottom the bolts on the axle proclaiming "There, now it's
tight enough." That sucks. Torque wrenches work.
If the cranks are not creeping farther up the taper (greased or not),
then what is causing the bolts to loosen after awhile? (<- honest question
looking for an accurate answer.)
I believe Jobst may have answered this awhile back....
- Jim
John Stone
> Much drivel about the grease no grease thing deleted...
>
> > Never, Never, Never put grease on the crank axle.
> >
> > Hope this helps,
> >
> > John Stone
> >
> >>>>
> BALOGNA! Submit some proof that this actually does happen. I've tried
it both ways and have found
> the above to not be the case. ANY crank arm that has been properly
tightened and left on the bike for
> an extended period before removal (say a couple years) is going to be a
bitch to remove. A thin layer
> of grease on the tapers will keep any possible corrosion caused by the
two dissimilar metals from
> becoming a problem. It WILL NOT make the crank arm slide further up the
spindle when tightened.
> Crank arms are not made of play dough.
Jim,
Your right crank arms are not made of playdough, but I've seen my fair
share of wollowed out crank arms that come from various shops in our area
that use grease on the crank arms, and customers that say "well,.that
other shop said to put grease on the crank arms".
The thin layer of grease does not stop corrision of disimiliar metals it
actually helps it happen. Actually if the crank arm is put on properly at
the correct torque setting then you should have no roblem removing the
crank arm, no matter how long its been on the crank.
Check out Joshua Putnam post about the Suntour Engineers and what they
found out, if you check out a "Good Professional Shop" they do not grease
the crank axle.
Sorry to continue this topic.
Outta here,
John Stone
D Lecuyer
>From: Jeffrey Potoff <jpo...@cheme.cornell.edu>
>Subject: Re: Cranks on Axles - to grease or not?
>Date: Thu, 20 Jul 1995 13:15:08 -0400
>On Thu, 20 Jul 1995, John Stone wrote:
>> Never, Never, Never put grease on the crank axle.
>fit on the BB axle, held in place by the crank bolt, how on earth would
>grease on the BB axle allow the crank to move ?
>Jeff
Pardon me, I just cut into this thread and I'm probably stating something
that has already been stated but:
In this world nothing is perfect. Aluminum and steel will always stretch
when more stress is applied to them, until they start deforming. Putting
grease on BB reduces the amount of friction between the interface of the arm
and axle and does allow the crank arm to move more freely than if no grease
was applied. This also allows the crank arms to round out more easily.
Even if the crank bolt is tight, the extra force applied by the rider can
cause the arm to move, hence to minimize this, don't grease axles. (I've
waisted a crank set because of greasing. I was able to tighten so much
that my bolt bottomed out against the BB. Now that my crank has worked
itself loose again, I have to buy a new one because I can't tighten it up
anymore.) May you learn from my mistake.
------------------------------------------------------------------------------
Daniel J. Lecuyer
University of Waterloo
Waterloo, Ontario, Canada.
John Stone
> I've had my current road bike since mid-1988, roughly 10k miles. I've
> always lightly greased the BB tapers, and I haven't had any problems with my
> cranks. They haven't moved up the tapers, the bolts have not come loose,
> etc.
>
> Maybe all the ones you've seen that were screwed up had the bolts torqued
> way too high, or they were ridden when they were loose on the BB, which
> messed up the holes in the cranks?
The several people who have made the comment that they lightly grease the
taper of the BB axle just from there postings sound like they do all their
own maintenance. Periodically checking their bikes over for problems and
most likely are "in tune" to how there bikes feel and any changes that
they have (The key to stopping most bike problems). Which 95% of the
cycling populace doesn't do or know how to do.
If it works for you, go for it.
Have fun,
John Stone
Alex D Rodriguez
D Lecuyer <DLEC...@MECHANICAL.watstar.uwaterloo.ca> wrote:
>waisted a crank set because of greasing. I was able to tighten so much
>that my bolt bottomed out against the BB. Now that my crank has worked
>itself loose again, I have to buy a new one because I can't tighten it up
>anymore.) May you learn from my mistake.
Can you please give us mroe details on how you ruined your crank? When you
say you were able to tighten it so much, was it at the time of the initial
install or was it when you retightened the bolts after riding since they
were loose? Before we can learn from your mistake we need to get more details.
Thanks.
-----------------
Alex __O '86 Dodge Omni GLH Turbo
_-\<,_ '87 Alfa Romeo Milano
(_)/ (_) '88 Vitus/Dura-Ace
David Kohli
ultimately not get anywhere, (two tribes, each claiming truth). But I can
not resist the temptation to put my spin on it.
There was a shop (it is no longer) that I worked at here in Madison where
when things got slow we made a point of debating every issue of bicycling,
and for a while "to grease spindles or not" was a regular subject. We
often tried to settle our differences of opinion by citing accepted
experts. For this one consulted tech reps from Shimano, Campagnolo, and
Suntour. All three said "install cranks without grease", when asked why
they tended to say something about overtightening. None of them felt
corrosion was was a consideration.
That ended the open battle at the shop, but some of us continued to grease
anyway (not me, I was a committed nongreaser from the begining).
I will not say that the component manufacturers reps own the "truth" I
offer it as a suggestion with the knowledge that there are many cranks
greased and dry serving their owners well.
ps Just to add a tone of confrontation I also will say that even here in
wisconsin I have never encountered a crank/bb where corrosion was a
problem.
Calvin Rickard
> Never, Never, Never put grease on the crank axle.
>
> Hope this helps,
>
> John Stone
>
>>>>
>>BALOGNA! Submit some proof that this actually does happen. I've tried it >>both ways and have found
>>the above to not be the case. ANY crank arm that has been properly tightened >>and left on the bike for
>>an extended period before removal (say a couple years) is going to be a bitch >>to remove. A thin layer
>>of grease on the tapers will keep any possible corrosion caused by the two >>dissimilar metals from
>>becoming a problem. It WILL NOT make the crank arm slide further up the >>spindle when tightened.
>>Crank arms are not made of play dough.
>>Jim
Jim you're correct about some bottom bracket axles & crank arms are different
metals. For instance - steel axle and aluminum crank arms. The mating of
these two metals cause combined with the action of peddeling causes friction,
and heat build up between the two different metals. The Aluminum cranks (being
a softer metal than steel) will begin to wear, small fragments of aluminum will
appear on the steel axle. This wearing process is minute and not really a big
deal unless you add grease to the equation. Grease is an excellant lubricant,
However even grease breaksdown especially when exposed to heat. When this
happens the grease and the grit that collects in grease begin to increase the
amount of friction between the two different metals and accelerates the wearing
process on the softer metal ( the crank arm ).
In the case where the crank arm and the axle are titanium the friction
generated can cause the crank arm and the axle to fuse/weld together. In this
case I'd recommend contacting the manufacturer about a way to avoid this from
happening. You could also try a anti-seize product to reduce the risk of
fusing/welding of the two components. (consult with the manufacturer first).
By all means avoid applying grease to the bottom bracket axle. Corrosion can
be temporarly eliminated with WD-40 or a fine grain of sand paper.
o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=
calvin rickard ahdnn1a...@eds.com
o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=o=
Kristan Roberge
>
> In article <3ug1rj$2j...@unixfe.rl.ac.uk>, m...@unixfe.cc.rl.ac.uk (Mike Ellwood) writes:
> |> At the risk of starting a controversy
> |> (which is _not_ my intention)
> |> what are people's feelings about greasing axles
> |> before fitting a crank?
>
>
> Subject: 8.45 Installing Cranks
> From: Jobst Brandt <jbr...@hpl.hp.com>
>
>
> The admonition to not lubricate the tapers of the crank spindle seems
> to find life only in bicycle cranks among all the machines I have ever
> seen. I have never heard a mechanical or metallurgical explanation
> for this "dry assembly" instruction.
Oh good. A valid opinion on the subject. I don't think the dry-cranks
method would be as bad if mountain bike action didn't always spew out
'we put our cranks on bone dry' whenever this topic comes up in a
reader letter or article. More mountain bikers believe what's printed
in that magazine than in any other publication (which is too bad,
I've found mountain bike and MTB to be better - more reliable - sources
of info).
I myself use a light amount of grease on my Ti BB spindles to silence
the creaking noises that are amplified thru my aluminum frame. The
best explination yet for this problem with Ti BBs is that the Ti 6/4,
having a sharper edge on it than a chromoly spindle (which is forged)
from the machining process, cuts into the crank taper every time you
install your cranks. Each cut generates tiny flakes of aluminum which
are the source for the noise. The solution is to remove the cranks.
Clean the tapers (of both cranks and spindle with steel wool, then apply
a thin layer (maybe a finger tip's worth) of hi-pressure automotive
grease to keep the Ti spindle from slicing into the crank again. This
is at best, a temporary fix, but it does silence the noice for a few
weeks to several months.
JOHNMAC*DOUGALL TRIUMF OPERATIONS
ten years ago at Rocky Mountain. The aluminum crank and cro-mo spindle
provide a '+1, -1' valence bond that would be insulated by the grease".
The procedure for crank installation is to degrease the crank and spindle
with alcohol, then mount the crank on the spindle and tap it with a mallet
to seat it, then install a well oiled (or greased) bolt to the correct
torque (30 lb-ft). Retorque after one hour and after ten hours.
To remove a crank, thread the crank puller into the crank (finger tight),
tighten the bolt to tension the puller, then tap the bolt with a mallet to
release the crank. It is important to not "drag" the crank off the spindle
when tightening the bolt but to "pre-load" the puller and let the shock of
the mallet blow release the crank.
Joshua_Putnam
>Bob Podeur of Pacific Northern Bicycle Factory said "we dealt with this
>ten years ago at Rocky Mountain. The aluminum crank and cro-mo spindle
>provide a '+1, -1' valence bond that would be insulated by the grease".
This is getting more out to lunch every day! First we had people
claiming grease would let the cranks wear out, even though
perfectly dry cranks still squirm on steel tapers. Now we're
supposed to believe that the mechanical press-fit taper depends
on "a '+1, -1' valence bond" rather than on the well-documented
mechanical characteristics of taper joints.
Sounds like the market-droid fluff in the bicycle rags, not
competent engineering.
>The procedure for crank installation is to degrease the crank and spindle
>with alcohol,
I put a dollop of my bicycle grease in a dish of alcohol last
night, and it hasn't dissolved enough to color the alcohol. This
is supposed to degrease a spindle?
Joshua_Putnam
>For instance - steel axle and aluminum crank arms. The mating of
>these two metals cause combined with the action of peddeling causes friction,
>and heat build up between the two different metals.
>Grease is an excellant lubricant,
>However even grease breaksdown especially when exposed to heat.
Now I'm supposed to believe that there's a significant problem
with heat breaking down the grease between a large aluminum heat
sink and a heavy steel spindle? What insulates the joint to keep
this heat from dissipating uniformly through the crank arm, or am
I just lucky to have avoided blistering my ankles all these years?
Mike Iglesias
Calvin Rickard <crickar> wrote:
>Jim you're correct about some bottom bracket axles & crank arms are different
>these two metals cause combined with the action of peddeling causes friction,
>a softer metal than steel) will begin to wear, small fragments of aluminum will
>appear on the steel axle. This wearing process is minute and not really a big
>deal unless you add grease to the equation. Grease is an excellant lubricant,
>However even grease breaksdown especially when exposed to heat. When this
>happens the grease and the grit that collects in grease begin to increase the
>amount of friction between the two different metals and accelerates the wearing
>process on the softer metal ( the crank arm ).
So what happens to the "grit" if there's no grease there? Does it vanish?
What kind of heat buildup are we talking about here? It seems like it would
have to be pretty high to cause grease to break down. And how fast is the
crank going to wear out with this "grease and grit"? 5k miles? 10k?
Jobst Brandt
science and a general misunderstanding of how the press fit on a
square taper transmits torque.
One claim is that grease in the interface will cause the crank to
rotate on the spindle and ruin the bore as it works loose. What is
ignored is that the torque in this interface is transmitted by the
pressure on the faces of the square shape, not by friction. Any
friction in this joint is overcome by elastic fretting of the softer
metal (Aluminum) on the steel. Besides, lubricant that was put on the
flat faces to facilitate a predictable press for a given retaining
screw torque will have been displaced in a short riding distance.
This fit is a classic place where fretting readily disperses
lubrication.
The argument that the lubricant acts as corrosion resistance is
wishful thinking. As mentioned above, the interface retains no
lubricant during the practical life of the junction. The grease or
oil is there only for the purpose of installation to prevent galling
as the crank is pressed into place.
That there is no significant lubricant in the interface when in use is
evident from the presence of fretting corrosion upon removal of a well
used crank. The faces of the steel spindle show rouge and typical
fretting damage.
For this press fit to work properly, the pressure must be great enough
to prevent elastic separation between the crank and spindle under
torque, bending, and shear loads. This means that in an exaggerated
visualization of such a joint made of a steel spindle and a rubber
crank, should open no gap when putting force on the pedal. Friction
has no effect on this distortion because the two components fret into
a position of pressure equilibrium in a few load cycles.
Failure of this interface occurs when the press is too lose and a gap
opens between spindle and crank. If a gap opens, the bore will
plastically deform from the resulting concentrated load in the
remaining small contact zone. Torque is transmitted by the entire
face of the press fit, both the leading edge whose contact pressure
increases and the trailing edge whose contact pressure decreases. If
lift-off occurs, the entire force bears only on the leading edge and
plastic failure ensues. Tightening the retaining screw afterward
cannot remedy the failure because the crank bolt will break before the
spindle can exert sufficient stress to re-establish a square hole in
the crank. Besides, the crank would split before any plastic
deformation could occur even if the screw were sufficiently strong.
A side effect of the squirming fretting motions that occur is that
once the cranks have been substantially loaded, the retaining screws
appear to have loosened. However, the screws did not unscrew but
instead the crank moved away from the retention face of the screw as
it deformed under load. The left crank does this more than the right
crank because it experiences greater stress in use.
The junction of the left crank and spindle experiences torque and
bending simultaneously. The bending load arises from the lateral
distance from pedal to the end of the spindle. In contrast, the right
end of the spindle transmits either torque from the left crank or
bending from the force on the right pedal, but not both at the same
time. Torque from the right pedal goes directly into the chain
without affecting the crank and spindle joint.
If the apparent looseness of crank bolts is taken up by repeated
tightening, the cranks will ultimately split, usually through two
corners of the square taper. A recent article in a European magazine
showed such a failure and attributed it to overtightening on
installation and alluded to lubrication as the culprit. This is
highly improbable because the retention screw will fail before the
crank is damaged. Wheelsmith bicycles has a classic example in their
collection of "interesting" component failures of a Campagnolo Record
crank that failed from repeated tightening.
Because retaining screws could become entirely lose from squirming
action, especially if the press is relatively light, "dust caps"
should be used to prevent screws from subsequently unscrewing and
causing crank failure. Besides, the loss of the screw won't be
noticed until the crank comes off, long after the screw fell out.
Jobst Brandt <jbr...@hpl.hp.com>
Tom Younger
In a previous article, crickar (Calvin Rickard) says:
>com!usenet
>From: Calvin Rickard <crickar>
>Newsgroups: rec.bicycles.tech
>Subject: Re: Cranks on Axles - to grease or not?(NOT!)
>Date: 26 Jul 1995 21:38:54 GMT
>Organization: General Motors Corporation
>Lines: 43
>Message-ID: <3v6cle$r...@mloeff01.elec.mid.gmeds.com>
>References: <jstone-2007...@dp012.ppp.iglou.com> <3ulj38$18...@news.gate.net>
>NNTP-Posting-Host: 130.172.18.4
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>X-URL: news:3ulj38$18...@news.gate.net
>
>Much drivel about the grease no grease thing deleted...
>
>> Never, Never, Never put grease on the crank axle.
>>
>> Hope this helps,
>>
>> John Stone
>>
(* Snip! *)
>
>>>Jim
>
>Jim you're correct about some bottom bracket axles & crank arms are different
>metals. For instance - steel axle and aluminum crank arms. The mating of
>these two metals cause combined with the action of peddeling causes friction,
>and heat build up between the two different metals. The Aluminum cranks (being
>a softer metal than steel) will begin to wear, small fragments of aluminum will
>appear on the steel axle. This wearing process is minute and not really a big
>deal unless you add grease to the equation. Grease is an excellant lubricant,
>However even grease breaksdown especially when exposed to heat. When this
>happens the grease and the grit that collects in grease begin to increase the
>amount of friction between the two different metals and accelerates the wearing
>process on the softer metal ( the crank arm ).
>
The square drive elimanates any movement between the parts. Therefore,
the only heat produced by the peddeling action is from internal friction
in the metal -- if you flex a peice of metal, it will heat up. However,
this bending is miniscule, therefore the heat buildup is negligable.
How is one piece of metal going to wear if there is no movement between
them??? Well, nothing wears. Also, you are saying that a lubricant will
increase the wear rate of two metals. This does not make sense. Do you
run all your bearings dry, since they will heat up MORE than your BB
spindles, following your (logic), you shouldn't put grease anywhere on
your bike, except maybe on your rims or brake pads.
>In the case where the crank arm and the axle are titanium the friction
>generated can cause the crank arm and the axle to fuse/weld together. In this
>case I'd recommend contacting the manufacturer about a way to avoid this from
>happening. You could also try a anti-seize product to reduce the risk of
>fusing/welding of the two components. (consult with the manufacturer first).
>
Where do you ride your bicycle??? I don't regularly see glowing red
bottom brackets (generally, steel will glow red when you are welding it),
but I would sure like to see some!!! That bike must REALLY flex and that guy
must be REALLY strong in order to generate that much heat in the BB.
Also, have you ever tried to weld aluminum??? You will find aluminum has
a very small heat range between where you can weld it and the whole thing
turns into a puddle. I've never seen anyone riding along and suddenly
had thier crank melt since they greased thier bottom bracket
>By all means avoid applying grease to the bottom bracket axle. Corrosion can
>be temporarly eliminated with WD-40 or a fine grain of sand paper.
>
Following your logic, I would agree with you, but your logic is totally
illogical. If the parts did move against one another (which they don't,
because of the press fit of the square drive) then grease would help
lubricate the joint, which you would want, but this does not even move.
You still want grease, however, in order to ease assembly and
disassembly. The grease has no function other than perhaps displacing
god knows what when assembled, but it sure makes it easy to assemble and
disassemble later.
By all means, use grease, and don't sand your parts. You will just make
the fit worse, and then you may run into problems later with a wobbly
crank when you round out your hole.
BTW, read the FAQ.
--
TTTTT OO M M | Also known as: | |~~|
T O O MM MM | COMPTE...@CAMINS.CAMOSUN.BC.CA | @ o\
T O O M M M | Be young, have fun, | | _)
T OO M M | and drink lots of beer!!! | \__O --HI!!!
Tom Younger
In a previous article, jbr...@hpl.hp.com (Jobst Brandt) says:
>Much of what flies around this topic is BS that is based on half baked
>science and a general misunderstanding of how the press fit on a
>square taper transmits torque.
Yup.
(* Mega snip! *)
>
>The junction of the left crank and spindle experiences torque and
>bending simultaneously. The bending load arises from the lateral
>distance from pedal to the end of the spindle. In contrast, the right
>end of the spindle transmits either torque from the left crank or
>bending from the force on the right pedal, but not both at the same
>time. Torque from the right pedal goes directly into the chain
>without affecting the crank and spindle joint.
>
Although I agree with all of your post, I believe this is a bit of
oversimplification here. Often times, I will ride with my butt out of
the saddle and not be pedalling, like when off-roading down a scary hill,
etc. This will transmit both torque and bending through the bottom
bracket, since I have my cranks horizontal, and am not pedalling. Mind
you, the torque is all backwards on the axle. However, it is true if you
ONLY pedal, and never stop, what you say is purley true.
>If the apparent looseness of crank bolts is taken up by repeated
>tightening, the cranks will ultimately split, usually through two
>corners of the square taper. A recent article in a European magazine
>showed such a failure and attributed it to overtightening on
>installation and alluded to lubrication as the culprit. This is
>highly improbable because the retention screw will fail before the
>crank is damaged. Wheelsmith bicycles has a classic example in their
>collection of "interesting" component failures of a Campagnolo Record
>crank that failed from repeated tightening.
>
>Because retaining screws could become entirely lose from squirming
>action, especially if the press is relatively light, "dust caps"
>should be used to prevent screws from subsequently unscrewing and
>causing crank failure. Besides, the loss of the screw won't be
>noticed until the crank comes off, long after the screw fell out.
Couldn't you just lightly tighten the bolts just enough so that they
wouldn't fall out, but don't re torque them??? Or, alternatively, why
not just use lok tite???
Mike Jacoubowsky
>>
>>Much drivel about the grease no grease thing deleted...
>>
>>> Never, Never, Never put grease on the crank axle.
>>>
>>> Hope this helps,
>>>
>>> John Stone
>>>
the special mechanical properties involved, the torque, or anything
else like that.
What I *DO* know is this:
In our early days, we sold a lot (I mean HUGE NUMBERS) of $300+ bmx
bikes with aluminum cranks (mostly early variations of a Shimano 600).
We *NEVER* greased the spindles, and had very, very few come back in
rounded-out. The shop down the street greased ALL of their spindles,
and we saw their bikes all over the place with cranks coming off. The
numbers involved in each case are large enough that I don't think it's
a matter of their customers being harder on the bikes than our
customers. Talking with other people confirmed that bmx-ers were
destroying cranks when grease was applied to the axles. The nice thing
about all of this is that the bikes got extreme use in a short period
of time...you didn't have to wait around for a year or two to find out
how something was going to work. (And aren't lessons learned by
observing somebody else's failures the very best type?)
Now, we haven't sold a "real" bmx bike in maybe 10 years or so...we
primarily sell lots of road & mountain bikes, and we continue to keep
the crank tapers (and axle flats) clean of grease...and very rarely
ever see a crank come in that's worn out (either rounded out or simply
pushed on too far).
I'm not going to spend time reading all the theoretical technical stuff
about why grease is good/bad. Plain simple experience tells me that my
shop is better off keeping grease away from crank & spindle flats.
If you really want to battle, I can offer only a slight compromise- Put
grease on the spindle, and then wipe it off with a rag. I suppose you
might get some slight residual grease left to do whatever good you
think it might do, and I doubt there'd be enough to do any harm.
James M. Reed (AA)
While I value Jobst's opinion, I don't think he would be willing to
replace cranks damaged from overtightening, undertightening or whatever.
The answer is simple, follow the manufacturers instructions on instalation.
Cook Bros. Racing "do not grease bb spindle before instalation...voids
warrantee"
Hmmmmm....
Ride Well
James
SBW
Joshua_Putnam
Sounds like just another excuse not to replace parts. Unless
they specify degreasing the spindle with a strong solvent (the
alcohol mentioned earlier in this thread won't degrease a spindle
at all), the spindle is most likely going to be greased anyway.
The average mechanic will have enough grease on his fingers to
grease the spindle.