Frequent removal/refitting of square taper crank harmful?

[Illaveago]

Thanks for some useful feedback folks. Looks like it's not a good idea, I'll find an alternative way to achieve what I want.

There is also the risk of you forgetting to tighten up the bolt/ nut and it could fall off just when you are applying a lot of force to it! Its not nice standing on the pedals when one gives way!

 

[Punkawallah]

How about the OP remove one-sided every day, leave the other side as the control sample, and report back in sixty years or so?

I see we have a man of Science! among us :-)

 

[Yellow Saddle]

Stick to the provisors

With the best will in the world, the removal and refitting of a taper chain set is not something that can be repeated infinite times, it just can't, and you know that. Each time introduces a minute deformation of the materials (and let's be honest, the softer aluminium of the chainset is the sacrificial material here, not the hardened steel spindle) until eventually the chainset will 'bottom out' on the taper and not be secured by the retaining nut/bolt. Even under laboratory ideal conditions where the chainset taper interface is scrupulously clean and fitted to the book torque this is not an unlimited process and the described mode of failure will eventually occur. It may be hundreds of cycles down the lifetime of the components, but it will happen, and this time is hastened by frequent unnecessary repetition.

Also, we have to factor in the lack of adherence to the ideal procedure. I work in an industry where machines are serviced by hours and, to pick an example, there are tools that may be serviced at 1000 HR intervals. This involves a fairly intrusive strip down and I can usually tell who did the previous service by how stupidly tight the fasteners are. This is a high-vacuum machine, it pretty much holds itself together once pumped down and the bolts are there just to keep things in place until the vacuum forces take over, but this doesn't stop highly paid and expensively trained 'engineers' from tightening the fittings way beyond any documented values.

Do we think the average bike shop or DIY mechanic can resist exceeding the specified torque for chainset bolts because they 'don't want the cranks to fall off'?

For all intents and purposes, taper chainset removal has limited repeatability. If someone is careful and sticks to best practice this might be hundreds of times. In less ideal conditions, but with some mechanical sympathy it will be double figures. Some ham-fisted feckwits will achieve single figures!

Well, nothing will survive infinite handling. So let's stick to "frequent" and, the provisors mentioned.

Within that range, the deformations you talk about are elastic, not plastic. In other words, each time it is torqued with the same force, it advances on the taper, to the same depth. Within the plastic range, this means that the crank will never bottom out. You have not demonstrated a mechanism by which your scenario is true.

The rest of your argument is just noise, I'm afraid. I've already spelt out the provisos.

But as an interesing aside. Did you know that you cannot break a square taper crank by tightening the bolt? Maybe someone here with a spare scrap crank and BB can try and prove me wrong.

 

[fossyant]

It would have helped if the OP had said he wanted to try out a few cranks and configurations before settling on one set. The answer would have been, fine go ahead. The post said regular swapping like it was ongoing.

Does really help if people are a bit more specific and not remain cryptic. Unless the OP is doing secret squirrelling to win next year's Tour.

 

[scotsbikester]

Thanks for some useful feedback folks. Looks like it's not a good idea, I'll find an alternative way to achieve what I want.

As I said less than half way through this thread. Some of you seem determined to continue arguing about any damage which may, or may not, happen. That's up to you I suppose, it's a free country. Some people seem unable to take "yes" for an answer. Though does rather remind me of:


View: https://www.youtube.com/watch?v=ohDB5gbtaEQ

or perhaps


View: https://www.youtube.com/watch?v=eH56UOjDQ4A&t=61s

 

[albion]

Should be safe, just be careful with the crank remover tool.
I recent had my first ever pedal cross thread. I knew the pedal was suspect removing, yet the left crank and pedal are now likely KO.

 

[C R]

^^ As I said about half way through this thread.

But thank you all, yet again, for opinions you have offered.

Interestingly, I see a lot more responses if I don't log on. Many of them disappear when I do log on.

But there are some interesting, and varied opinions offered. For those of you who were conjecturing at my competence, no, I am not a "qualified engineer". But as one poster has pointed out, to declare myself as one, or give greater credence to somebody who did declare themselves as such, would be a perfect example of the fallacy of an appeal to authority.

My approach to my work on my own bike (which I did build up from a naked frame, by the way) has been to follow all instructions scrupulously. I have 4 torque wrenches (3 clicker, one beam, for the LH threads). The larger clickers are Teng, which I believe are a fairly well respected brand. And although I haven't had them re-calibrated, I take care to slacken them to their lowest setting, they are stored in a warm house, and the only use they see is occasionally on the bike. I use Zinn as my reference for torque wrench settings. Maybe I am one of the "ham-fisted" idiots that others refer to, but having watched qualified "tradesmen" in all sorts of situations, I suspect I'm no more "ham-fisted" than some people who actually get paid for allegedly skilled work. I even torque things like cable clamps, stems etc. on. Recently, fitting a new rack, I followed Tubus' astonishingly precise torque setting of 4.3 Nm. Friends who make up their own bikes are astonished that I bother, but there you go.

I am also aware that there is, or at least used to be, some discussion around whether square taper spindles should be lubricated or not. As far as I can tell the current opinion is yes, but lightly. Which is what I do, but am careful not to exceed recommended torque settings, as it is so much easier to over tighten if lubricated. I hope I've never overtighted the crank. Yes, I also lubricate the bolt, lightly. I have a variety of lubricants and anti-seize compounds which I try to use appropriately. In the early days I obviously did under tighten a crank. As it became loose soon after making the bike up, I didn't ride it for very long before I found the error. I don't use that bottom bracket any more, or the cranks (I think).

Some of the feedback has been useful. My prediction is that the cranks will probably be on and off a few times, while I try out various options, make adjustments, and so on, and then will stay on either permanently, or change very infrequently, if at all.

As to "why" and my reasons for not disclosing, that is best explained if I give an example of an imaginary discussion on an internet forum, like this one, on any subject:

"Hi folks. I was think of replacing the discomknockerator on my bloggs and smith fuffle valve with a 42mm one. Will that work?"

"Why on earth would you do that. Good old 1.5 inches fuffle valves are fine. They were good enough when I were a lad, these new metric ones are rubbish"

or

"Nobody uses fuffle valves anymore. They are old hat, it's 2025 now grandad, fuffle valves were replaced with bluttering pins years ago"
or any variety of similar responses.

If one has the temerity to say why one wants to use a 42 mm fuffle valve - "so I can fit a durdle-pin" - then there follows a whole barrage of:

"Durdle-pins are only for amateurs, real furtle-wranglers don't use them"

or it's close cousin

"Durdle pins are only for professional furtle-wranglers, don't waste your money"

or a whole slew of why durdle-pins are a really bad idea. Even though fitting a durdle-pin wasn't actually the question.

Cheers

Eh?

 

[C R]

There is also the risk of you forgetting to tighten up the bolt/ nut and it could fall off just when you are applying a lot of force to it! Its not nice standing on the pedals when one gives way!

Been there, luckily I felt the crank wobble before anything untoward happened.

 

[silva]

The damage inflicted to the alu thread for the crank removal tool is likely an order bigger than the damage to the steel surfaces of the square taper.
That is, by the time the axle becomes unusable, 1000 cranks became unusable.

 

[mickle]

As I said less than half way through this thread. Some of you seem determined to continue arguing about any damage which may, or may not, happen. That's up to you I suppose, it's a free country. Some people seem unable to take "yes" for an answer. Though does rather remind me of:


View: https://www.youtube.com/watch?v=ohDB5gbtaEQ

or perhaps


View: https://www.youtube.com/watch?v=eH56UOjDQ4A&t=61s

Except, that the answer is 'no'.

 

[lazybloke]

Sod the damaged cranks/threads questions what about convenience?

Yellowsaddle very briefly mentioned a bottom bracket that's far easier to dismantle: hollowtech

I used cotter pins or square tapers for decades, and always found them a bit of a faff to remove for maintenance. Especially if all i wanted to do was to give the chainset and bottom bracket area a really good clean.



Finally in 2019 i got my hands on a bike with a hollowtech2 crankset, and hallelujah; so much easier; and i'll take that over the longer-term reliability of older options.

 

[Sharky]

In the olden days, when Stronglight 49D cranks were common, removal of the chainset was a regular event for some riders. If the chain fell off the small ring and found its way betwixt crank and bottom bracket there was no faster way of extracting it.

Think I've still got a pair of 49D's, together with a 54t, TA chain ring, in the garage!