Square taper spindle/crank and greasing

[[email protected]]

Someone writes:

>> You are assuming plastic deformation with each installation or use.

> That, or maybe something fatigue related. But it was meant as a
> straight question whether repeated assembly/disassembly was
> significantly harmful to a crank or not, that's all. I'm not
> launching any theories nor stating any preferences to a particular
> explanation, so it's assuming only to be able to pose the question.

>> That is not so, or all cranks would fail in short order....

> OK, question answered, thanks. So from here on I'm assuming that
> bike cranks have an indefinite life with regards to
> assembly/disassembly/reassembly, with no significant wear occurring
> from the actual assembly/disassembly process.

Unless you are a regular take-it-apart type of rider whether it needs
it or not, cranks are essentially longer lived than most riders.

>> ... I think you should review the explanation of how cranks get
>> split from repeated tightening.... I think I got that one, assembly
>> torque does NOT have to be the same as

> torque-during-use as you'll always see SOME slackening as the bike
> is being ridden. Hence an urge to always maintain assembly torque
> will eventually cause something to fail. The only thing it didn't
> tell me was whether there were any residual effects from previous
> assemblies, which by definition, would fit under the phrase of
> "re-tightening". After all, details and components that are only
> good for one, or a few assemblies can be found every now and then.

That's a good reason to make sure there is lubrication between crank
and spindle during installation even though it is no longer there
after use. If re-installation caused permanent damage, you should
find wear debris from that damage and it would need to occur during
installation because we know of many cranks that have been in place
for thousands of miles.

You might review the item on crank bolt loosening and to get a clearer
idea of the effect.

http://www.sheldonbrown.com/brandt/installing-cranks.html

Re-tightening crank bolts after proper installation can cause this:

http://pardo.net/bike/pic/fail-001/FAIL-001.html#crank-fail-011

Jobst Brandt

 

[datakoll]

Loctite's copper anti-sieze is some good compound. just squeeze tube
very carefully to mix intrenally then juice out the liquid until the
paste comes out.
That is snot grease.
HOW'S THAT FOR SKIRTING THE QUESTION?

secondly! I ben thru this like at 25 miles out 3-4 times and at 3AM
you know which is an immense PITA so my firend the Schwine mechanic
told me to use a seatpost at 1 foot over the allen wrench or 3/8ths
drive AND SCREW IT DOWN TIGHT.

and do that 2-3 times. like tight then tight again to make sure the
joining isnot slipping backward's as an IC head bolt torque routine.

This works. It even works fore a beer can shimmed taper.

Doijng that at a storage area, I elicited a shouting form a nearby
Alpha male with girlfriend about splitting the crank arm. I yam told
STCA is nearly impossible. But I went and bought out Wooley's supply
of left crankarms and the right cannot so....

that's a cool word no? doijing!

 

[datakoll]

BTW greasing threads is sooooooo 19th century. Threads are loctited
after carefully cleaning threads surfaces with thinner then CHOH not
greased. Wal sells adequate blue loctite. Let the lock set up in a
warm place for 24 hours.
Carefully Linseeding the outside bolt head or hex head surfaces
waterproofs the assembly. Grease, watersoluble unless marine and
marine is also soluble over time-3, 4 hours-linseed oil isnot as
linseed polymerizes. polymerizes. no kidding.
frankly, the best to do is throw the entire taper into the can and
start over with a MO octalink/BB for 70 bucks.

 

[still just me]

On 15 Feb 2008 00:09:08 GMT, [email protected] wrote:

>
>Re-tightening crank bolts after proper installation can cause this:
>
>http://pardo.net/bike/pic/fail-001/FAIL-001.html#crank-fail-011

Point of order: "retightening" wouldn't cause that, but
"overtightening" might.

 

[jim beam]

still just me wrote:
> On 15 Feb 2008 00:09:08 GMT, [email protected] wrote:
>
>> Re-tightening crank bolts after proper installation can cause this:
>>
>> http://pardo.net/bike/pic/fail-001/FAIL-001.html#crank-fail-011
>
> Point of order: "retightening" wouldn't cause that, but
> "overtightening" might.
>
>

absolutely.

 

[Peter Cole]

Andre Jute wrote:

> More commonly than you might think. You're looking at a whole bunch
> right now: the interface sockets on your computer are rated for a very
> limited number of insertions. I remember being so horrified by a spec
> that an RS232 port on a Mac was rated for only a 100 insertions (or
> something equally shocking)

A good point. In the aerospace industry, we often used "connector
savers", which were just back-to-back wired connectors installed (once)
onto flight hardware that stayed there through all the pre-delivery
testing. If you're worried about this sort of thing on your computer
equipment it would be easy to rig something similar.

For mechanical assemblies like cranks, it would seem there are only 2
possible sources for concern with repeated assembly: deformation and
wear. The former won't happen if the load doesn't go into the plastic
region (which it shouldn't) and grease takes care of the latter.

 

[Peter Cole]

Andre Jute wrote:

> Anyone with an ali bike should ask at his LBS to see the torque
> wrench. Mine didn't have one, and didn't use the one I bought to give
> him; I took over the work on my bike myself.

I'm not sure how many torque-critical fasteners there actually are on a
bike. Most threads are on the components rather than the bike, so an
aluminum (framed) bike isn't much different than any other. I'd use a
torque wrench on carbon fiber compression fittings, but that's about it.

Offhand, I can't see the particular danger of installing cranks without
a torque wrench. Too little torque and the crank may loosen (and ruin
it), too much and you may snap the head off the bolt. I think those are
the practical limits. I have torque wrenches, but I've installed square
taper cranks many times without one. It doesn't strike me as a critical
operation.

 

[Peter Cole]

still just me wrote:
> On 15 Feb 2008 00:09:08 GMT, [email protected] wrote:
>
>> Re-tightening crank bolts after proper installation can cause this:
>>
>> http://pardo.net/bike/pic/fail-001/FAIL-001.html#crank-fail-011
>
> Point of order: "retightening" wouldn't cause that, but
> "overtightening" might.
>
>

The mechanism Jobst is describing is the crank, when being loaded out of
plane by pedaling forces, levers against the bolt shoulder, causing it
to "squirm" up the spindle (permanently), resulting in loss of tension
in the bolt. By re-tightening and restoring the bolt tension to spec,
the process starts again, eventually putting enough stress into the
crank bore to split it.

Theoretically, you could do the same thing by over-tightening, but
according to those who have done it, you'll snap the bolt head off first.

 

[[email protected]]

someone writes:

>> Re-tightening crank bolts after proper installation can cause this:

http://pardo.net/bike/pic/fail-001/FAIL-001.html#crank-fail-011

> Point of order: "re-tightening" wouldn't cause that, but
> "overtightening" might.

I think you are guessing. Having watched crank bolts break from
overtightening, I am sure you cannot split a crank that way. If
you'll read the description of how cranks are split:

http://www.sheldonbrown.com/brandt/installing-cranks.html

you might get a clearer idea of how this occurs. The crank in the
picture above was split by re-tightening and I know the mechanic who
did it.

Jobst Brandt

 

[datakoll]

http://www.dukeathletic.com/supporters.html

 

[Andre Jute]

On Feb 15, 2:26 pm, Peter Cole <[email protected]> wrote:
> Andre Jute wrote:
> > Anyone with an ali bike should ask at his LBS to see the torque
> > wrench. Mine didn't have one, and didn't use the one I bought to give
> > him; I took over the work on my bike myself.
>
> I'm not sure how many torque-critical fasteners there actually are on a
> bike. Most threads are on the components rather than the bike, so an
> aluminum (framed) bike isn't much different than any other. I'd use a
> torque wrench on carbon fiber compression fittings, but that's about it.
>
> Offhand, I can't see the particular danger of installing cranks without
> a torque wrench. Too little torque and the crank may loosen (and ruin
> it), too much and you may snap the head off the bolt. I think those are
> the practical limits. I have torque wrenches, but I've installed square
> taper cranks many times without one. It doesn't strike me as a critical
> operation.

Turning the axle nuts on a hub gearbox in an ali frame without a
torque wrench is liable to cause damage. Chain tensioners on these
installations look something like an Egyptian ankh, with the circle
fitting around the axle between the dropout (actually in most cases a
trackracer slot rather than a dropout), and the sprocket on one side
and the roller brake on the other side. Torque the axle nuts on too
hard and you press these steel parts into the ali.

Andre Jute
Precision is a factor in the longevity of utility bike

 

[jim beam]

[email protected] wrote:
> someone writes:
>
>>> Re-tightening crank bolts after proper installation can cause this:
>
> http://pardo.net/bike/pic/fail-001/FAIL-001.html#crank-fail-011
>
>> Point of order: "re-tightening" wouldn't cause that, but
>> "overtightening" might.
>
> I think you are guessing.

no jobst, /you/ are guessing.


> Having watched crank bolts break from
> overtightening, I am sure you cannot split a crank that way. If
> you'll read the description of how cranks are split:

when are you going to learn that there's a difference between dynamic
loading and static loading? breaking a crank bolt is pure static load
as far as the crank is concerned. over-tightening [but below bolt
breakage] and then fatigue loading is what splits cranks. [along with
its anisotropy of course.]


>
> http://www.sheldonbrown.com/brandt/installing-cranks.html
>
> you might get a clearer idea of how this occurs. The crank in the
> picture above was split by re-tightening and I know the mechanic who
> did it.

what a cute little red herring - i hope you two are happy together.

but the fact still remains, just like your "stress relief" or "anodizing
cracks rims" theories, you have no clue about the science that explains
what you're observing. dynamic loading != static loading.

try not to inject ******** into your own knowledge vacuum, and then spew
it onto this forum as fact please. thanks.

 

[Tom Sherman]

datakoll aka gene daniels wrote:
>
> http://www.dukeathletic.com/supporters.html

Protecting your nuts from the squirrels, eh?

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

 

[still just me]

On 15 Feb 2008 18:00:22 GMT, [email protected] wrote:

>
>I think you are guessing. Having watched crank bolts break from
>overtightening, I am sure you cannot split a crank that way. If
>you'll read the description of how cranks are split:
>
> http://www.sheldonbrown.com/brandt/installing-cranks.html

If the supposition in that article is correct, then every ST alloy
crank would continually wear, require re-tightening, then wear some
more, then the cycle repeats.

Why don't all of them break then?

 

[[email protected]]

Someone writes:

>> I think you are guessing. Having watched crank bolts break from
>> overtightening, I am sure you cannot split a crank that way. If
>> you'll read the description of how cranks are split:

http://www.sheldonbrown.com/brandt/installing-cranks.html

> If the supposition in that article is correct, then every ST alloy
> crank would continually wear, require re-tightening, then wear some
> more, then the cycle repeats.

> Why don't all of them break then?

If you were to see an animated FEM (Finite Element Model) you would
see that the external shape of the crank changes without significant
motion between crank and spindle. I is this external distortion that
makes the crank creep away from the retaining bolt. The interface
motion that occurs is extremely small but still enough to erode the
facets of the spindle, aluminum oxide doing the erosion in the steel.
I have sample spindles that have eroded faces after thousands of miles
of use under higher than average loading.

The amount of wear is not significant for the parts although it could
probably be measured by where the crank fits when pressed on (with
lubrication) between new and used. However, the precision of these
bores is such that one new crank fits on a few thousandths of an inch
different from the next anyway. It is not a problem as millions of
bicycles have shown.

Jobst Brandt

 

[jim beam]

[email protected] wrote:
> Someone writes:
>
>>> I think you are guessing. Having watched crank bolts break from
>>> overtightening, I am sure you cannot split a crank that way. If
>>> you'll read the description of how cranks are split:
>
> http://www.sheldonbrown.com/brandt/installing-cranks.html
>
>> If the supposition in that article is correct, then every ST alloy
>> crank would continually wear, require re-tightening, then wear some
>> more, then the cycle repeats.
>
>> Why don't all of them break then?
>
> If you were to see an animated FEM (Finite Element Model) you would
> see that the external shape of the crank changes without significant
> motion between crank and spindle. I is this external distortion that
> makes the crank creep away from the retaining bolt. The interface
> motion that occurs is extremely small but still enough to erode the
> facets of the spindle, aluminum oxide doing the erosion in the steel.
> I have sample spindles that have eroded faces after thousands of miles
> of use under higher than average loading.
>
> The amount of wear is not significant for the parts although it could
> probably be measured by where the crank fits when pressed on (with
> lubrication) between new and used. However, the precision of these
> bores is such that one new crank fits on a few thousandths of an inch
> different from the next anyway. It is not a problem as millions of
> bicycles have shown.
>

red herring. wear is not fatigue or stress concentration.

 

[Peter Cole]

Andre Jute wrote:

> Turning the axle nuts on a hub gearbox in an ali frame without a
> torque wrench is liable to cause damage. Chain tensioners on these
> installations look something like an Egyptian ankh, with the circle
> fitting around the axle between the dropout (actually in most cases a
> trackracer slot rather than a dropout), and the sprocket on one side
> and the roller brake on the other side. Torque the axle nuts on too
> hard and you press these steel parts into the ali.

I'll have to take your word for that, I've never seen one.

>
> Andre Jute
> Precision is a factor in the longevity of utility bike

Only place I know of where "precision" could affect "longevity" might be
bearing pre-load, and those typically don't need a torque wrench.