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PostPosted: Wed Mar 13, 2013 4:48 pm 
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Joined: Thu Jun 23, 2011 11:25 pm
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Location: It's not easy being a dolphin.
Hollister, care to elaborate and share your technical views / knowledge?


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PostPosted: Wed Mar 13, 2013 5:14 pm 
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Location: South and East of York
always a little anti sieze. makes dis-assembly much more enjoyable.
don't over torque the crank bolts, just some advice


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PostPosted: Wed Mar 13, 2013 6:10 pm 
Gold Trader / MacRetro rider
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Location: Sunny Glasgow
...
edited till later


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PostPosted: Wed Mar 13, 2013 7:15 pm 
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Hi all, as we rapidly approach the 20th page of chasing our tails, i'll make an attempt - admittedly most likely in vain - to put this topic to rest (why does this feel like i'm putting my own neck in the noose? ...i ask myself). OK here goes:

Having enjoyed following this thread, the most prominent single argument from each camp which i noticed were as follows:

THE 'DRY' CAMP: "greasing the taper means the crank will be pushed too far onto the taper causing permanent damage to the cranks [supposedly leading to cracked cranks, loose cranks, creaking cranks etc]". This my friends is a complete and utter myth. Torque values exist and must be respected. Torque values of screwed fasteners are specifically chosen to achieve two aims, firstly to affect a sufficiently secure and lasting fixture and secondly to avoid permanent damage of the components which are subjected to the force resulting from the applied torque (i.e. not exceed the elastic limit of the materials involved). This means that if you assemble the thing PROPERLY you are not going to damage the cranks or the taper. Aluminium is not cheese. greased tapers are not going to magically change the elastic limit of the materials or the force applied by the tightened crank bolt. Greasing the tapers will not cause damage to a PROPERLY assembled bicycle and if anyone wants to suggest otherwise i respectfully request them to supply irrefutable evidence.
Just a little footnote: Many people (i'd venture to say almost everyone) who do not use a torque wrench over - rather than under - tighten their fastenings and do so by a considerable degree. I have seen this time and time again. Many folks who use a torque wrench for the first time are amazed at how soon/easily the CORRECT torque is reached.

THE 'GREASE' CAMP: "greasing the taper protects against corrosion and facilitates easier disassembly". This is 100% correct and is good engineering practice for a tapered and contoured/keyed shaft including but not limited to bicycles (BTW we are not talking about lathes so let's not start that again - completely different application and principle of the shaft's drive transmission). Furthermore, greasing the taper assists in preventing binding and material pick-up therefore leading to correct and full seating of the components.
Another little footnote: By 'grease' you can, in the case of a bicycle, consider anything which provides both lubricative and anticorrosive properties (copperslip, LM, molybdenum, graphite, virtually any decent grease or oil SP, HP, EP, whatever).

I probably sound biased because i do lightly grease my tapers (above statements is why i do!) but to show [attempted :wink: ] fairness to both camps i offer the following:

A bicycle is, from an engineering standpoint, a very simple machine. It's components are not subjected to extreme temperatures, pressures, vibrations, torques or forces. Hence the real answer to our shared dilemma is that it really doesn't matter very much. If it did matter the answer would be gospal and there would be 1 page of consensus instead of 20 pages of arguing and the manufacturers of bike parts would all be singing the same tune. Chainline differences (if any) caused by dry or greased fitment are so miniscule as not to matter one iota in practice.

So my dear friends i wish to say how much i've enjoyed this discussion and now that i have the noose around my neck, who will be first to step forward and kick the wobbly chair from under me? :lol:


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PostPosted: Wed Mar 13, 2013 7:37 pm 
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I too grease my bb axles though after reading this thread it does occur to me I've never stripped a factory-assembled bike that had (visible) grease on the tapers. Hmm.

SP


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PostPosted: Wed Mar 13, 2013 9:39 pm 
Gold Trader / MacRetro rider
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Location: Returning
Roll up roll up , page 20 beckons


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PostPosted: Wed Mar 13, 2013 11:43 pm 
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Location: It's not easy being a dolphin.
RadNomad, cracking summary there. Now I'm not going to kick the chair because I'm in complete agreement, BUT

"It's components are not subjected to extreme temperatures, pressures, vibrations, torques or forces."

I fear the word "extreme" is too subjective, relative, undermines the seriousness of our beloved toys and you may be speaking for yourself / your own riding habits and environment.

Me, I'm a little lardy around the midriff in a healthy sort of way (cough..), ride in -10c, ride in +35C, ride in damp / wet weather, ride dry weather, ride on dusty gravel hardpack, gloopy mud, snow and ice, ride on bumpy XC terrain, occasionally ride off and up kerbs, ride on potholed roads, do the occasional +150 Km epic, irregular commutes to work, irregular commutes to the shops loaded with groceries, generally climb off the saddle on the big ring just like Bernard Hinault, and if all that wasn't enough I hardly ever clean the bike. When tugging on bar ends there can be a bit of pressure build up especially after a Guinness and some chicken mango pasta the night before. As a result and example of the sheer unrelenting extreme torture the bike is subjected to a quality 1995 World Cup level Parkpre Ti frame as recently cracked at the BB shell - chainstay weld :( . On a positive note, the cranks never creaked or fell off. I for one doubt even space ships aren't subjected to the full spectrum of extremities and magnitude as a humble square taper interface must endure.

:facepalm: ... page 20?


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PostPosted: Thu Mar 14, 2013 1:50 am 
Old School Hero

Joined: Mon Dec 26, 2011 4:41 am
Posts: 193
Location: Michigan, USA
The Ballad of the Ungreased Taper (in 3 part harmony)

In the year 2013
Assembled here the uninformed,
In the day when their cranks were dry...
and a 'dollop" (or was it wallop?) was applied
to the drive and non-drive side,
so in RB hell they shall not fry.

Yet the No minions sought release
for their right to be sans grease
and fought to have fair say,
so the RB bastions they did storm, until their views became the norm
and the thread still runs to this day.

Refrain...
Did you grease that crank, did you torque it properly
Are you sure it was correctly done?
We are twenty pages in,
But no closer to a win,
For the thread, still ahead, bloody fun.

In the year of 2013
assembled here the RB volunteers
in an attempt at The Great Compromise...
the words were eloquent
as the spokesman did his stint
with nary a word to antagonize

Ye readers don't dismay
It will live another day
Once again
into the breach
but growing wise

Or are we?


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PostPosted: Thu Mar 14, 2013 3:15 am 
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Hi Woz, yes you're right to question this since a bicycle is certainly subject to variations in operating conditions. What i mean by "not extreme" is:
Temperature: For a bike we are talking a modest range of ambient temperatures, not hundreds or even thousands of degrees which some other machines experience.
Pressure: Bikes operate in a pressure environment of approximately one atmosphere (depending on your altitude) and the variations are quite small, not the hundreds of BAR which some other machines experience. BTW I'm talking about the pressure experienced by the cranks/taper not the tyre pressures! :wink:
Torque: Without calculating the Nm (torque) one human can apply to a cycle crank, just consider that a human is developing only a fraction of one horsepower so while the torque is not inconsiderable, it is peanuts compared with many powered machines.
Vibration: Vibrations create sound (air pressure waves) and so in laymans terms this gives a feeling about how much vibration is really going on relative to other machines. Bicycles are not exactly noisey even when being raced on or off road (unless you crash maybe!). Plenty of other machines will remove your fillings if you lean/sit on them!
So i don't mean to belittle the humble bicycle or the enormous power of all us weekend warriors out on the trail :mrgreen: i just try to put the bicycle into context across the spectrum of engineering challenges. The more extreme the situation the more critical the materials/machining/assembly criteria. Our bikes are pretty basic gadgets as much as we may love and admire them, so riders can grease tapers if they want or stay dry if they want, it really doesn't matter much and it won't spoil our bikes either way as long it's assembled properly (see above post) and we don't ride them to the sun and back.


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PostPosted: Thu Mar 14, 2013 8:43 am 
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Joined: Mon Mar 28, 2011 9:29 pm
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Location: Somerset
RadNomad wrote:
The word ‘interference’ in your sentence, presumably quoted from another source, does not refer to the type of fit but simply says an interference is created between the two surfaces – which is actually obvious. This is an important distinction. Any two surfaces when secured together, especially with load (a force of some kind like bolt, clamp, pressure etc), will create interference between those surfaces but this in itself does not make it an interference fit. The term “interference fit” means that the security of the fixture is achieved by the interference between the two components. If this were true for bicycle cranks then everybody could permanently remove their crank bolts in full confidence that their cranks would not fall off while riding. Of course we know this to be not the case and the reason why not is because a bicycle crank taper assembly is not an interference fit, it is a clearance fit secured fast by a bolt (or sometimes a nut). Weight weenies worldwide would rejoice if crank tapers were interference fits because they could all save a few grams and almost certainly would’ve been doing so already since decades. This is a nice discussion but please let's not fly in the face of facts. This is engineering fact not just an opinion and if anyone insists on continually disagreeing with fact then OK go ahead.. :roll:


This is not fact.

An interference fit is one that stays together after assembly due to the distortion of one or both mating parts (or more), as a sqtp crank does.

In your example above a washer under a bolt is an interference fit, but when you remove the bolt it comes loose, this is not an interference fit.

Saying that bicycle cranks loosen during use without the bolt only further proves that the assembly is an interference fit. Guess what, an interence fit can be disassembled with force, whether that force is pedalling or a crank puller is irrelevant.

Look at the link from SKF's website, they clearly state taper fit bearings are an interference fit held together with some form of fastener.

Edit - this sums it up nicely - http://en.wikipedia.org/wiki/Interference_fit


Last edited by gtRTSdh on Thu Mar 14, 2013 9:57 am, edited 1 time in total.

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