not broken one of these Shimano BBs before

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tb
Posts: 129
Joined: 10 Jan 2007, 12:51pm

not broken one of these Shimano BBs before

Postby tb » 1 Oct 2020, 9:36pm

this is in no way a criticism of Shimano components as I am a big fan, having used their stuff since the mid 70's.

In my opinion Shimano - very durable, well machined and more competitively priced than some ever so lardy-dah Italian items.

this tapered axle snapped off after more than 15,000 miles but amazingly the bearings are as good as new, unfortunately the crank wasn't salvageable either as the tapper had damaged the inside of the alloy.
Image Attachments
Sminano BB_3.jpg
Sminano BB_1.jpg

Brucey
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Re: not broken one of these before

Postby Brucey » 1 Oct 2020, 9:43pm

I have seen that happen only very rarely on a shimano BB spindle. It seems more common with some other brands.

When I see this sort of failure it is usually obvious that fatigue has been at work. However it isn't clear how much contribution there has been from corrosion, both to initiation and propagation of the crack.

BTW it may not be obvious but the peak torque in that part of the spindle arises when you push hard on the LH pedal. Pushing hard on the RH pedal creates a bending load in the RH end of spindle but not a large torque.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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NATURAL ANKLING
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Re: not broken one of these before

Postby NATURAL ANKLING » 1 Oct 2020, 10:02pm

Hi,
Might not be the case but if the bolt was bottoming out in the thread not necessarily the hole which is not tapped all the way down.
This wouldn't be favourable.
Wrong bolt wrong hole, and or worn taper on the right hand crank.
NA Thinks Just End 2 End Return + Bivvy
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hamster
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Re: not broken one of these before

Postby hamster » 2 Oct 2020, 9:48am

Brucey wrote:BTW it may not be obvious but the peak torque in that part of the spindle arises when you push hard on the LH pedal. Pushing hard on the RH pedal creates a bending load in the RH end of spindle but not a large torque.


Moment of revelation why left hand cranks always strip! :D
I had always lazily assumed it was less metal around the taper interface, but of course it's the loading.

Bonzo Banana
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Re: not broken one of these before

Postby Bonzo Banana » 2 Oct 2020, 10:46am

If the inside of the crank arm is damaged by the taper doesn't that mean the fitting wasn't tight enough and therefore there was some movement in use which would have also created a lot of fatigue on the bottom bracket axle end to cause it to break eventually. It might have been a very small amount of movement maybe not even notice-able. These things happen I've had many a bottom bracket bolt work a bit loose over time but whenever it gets even slightly loose it clearly puts much more stress and wear on the components. Bottom bracket axles are hardened chromoly steel I think for good quality models and I doubt they ever bend the result of constantly flexing would surely be a break like that.

As a heavy rider who grinds/mashes I'd be pleased to get 15k out of a bottom bracket I must admit. Sometimes when I've tried non Shimano bottom brackets they only last a few months in the past and a complete false economy. Seem to recall I've had good results with both UN26 and UN55 bottom brackets. Even if I go cheap on other components I find something re-assuring about making sure I have a Shimano bottom bracket fitted.

Brucey
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Re: not broken one of these before

Postby Brucey » 2 Oct 2020, 11:05am

Bonzo Banana wrote:...As a heavy rider who grinds/mashes I'd be pleased to get 15k out of a bottom bracket I must admit. Sometimes when I've tried non Shimano bottom brackets they only last a few months in the past and a complete false economy. Seem to recall I've had good results with both UN26 and UN55 bottom brackets. Even if I go cheap on other components I find something re-assuring about making sure I have a Shimano bottom bracket fitted.


my guess is that enough of the taper was still inside the crank when the failure occurred that this chewed the crank up. IME it is rare that such a failure occurs outside of the crank taper entirely.

If you want nice reliable UN55s or similar, buy them now while you still can (just); they are being replaced by something else, cheaper and worse looking.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

rogerzilla
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Re: not broken one of these before

Postby rogerzilla » 2 Oct 2020, 1:51pm

Things that break in torsion classically have a spiral-shaped fracture. That's not a bad example.

bgnukem
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Re: not broken one of these before

Postby bgnukem » 2 Oct 2020, 2:50pm

Pretty bad corrosion on that bracket!

Would be interesting to examine the fracture surfaces to determine where failure initiated, i.e. from the taper surface or internal threads, any corrosion pitting or fretting wear, etc.

It's probably a fatigue failure as Brucey suggests. At work I often see fretting initiating fatigue cracking, so enough small movements with the joint slightly loose could be enough to start fatigue cracking. Throw in some iron oxide from the corrosion and you have a highly abrasive third body between the crank arm and axle, though any wear debris from either part will quickly oxidise to produce a highly abrasive substance in any case (iron oxide or alumina).

Shame Shimano are discontinuing the UN55, I assume it's too reliable and long-lasting for their liking! Having recently written off a Token carbon-shelled BB after just ONE wet ride, I'm wondering what is the best option for square taper brackets in the future?

As well as 107mm, I also use 103mm axles which weren't available in UN55.

hamster
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Re: not broken one of these before

Postby hamster » 2 Oct 2020, 3:51pm

bgnukem wrote:Shame Shimano are discontinuing the UN55, I assume it's too reliable and long-lasting for their liking! Having recently written off a Token carbon-shelled BB after just ONE wet ride, I'm wondering what is the best option for square taper brackets in the future?

As well as 107mm, I also use 103mm axles which weren't available in UN55.


You and me both with a Token, although mine took a winter on my singlespeed MTB.

I like ones which take industrial bearings to rebuild: Shimano UN90/91 and Real Designs Crankcase are two that can be rebuilt and bought secondhand. I think also Phil Wood; and finally Royce if you want something from the home team. I'm running a Royce now.

MikeF
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Re: not broken one of these before

Postby MikeF » 2 Oct 2020, 4:20pm

Brucey wrote:
If you want nice reliable UN55s or similar, buy them now while you still can (just); they are being replaced by something else, cheaper and worse looking.

cheers
Are Shimano still going to make BB or are they stopping production entirely?
"It takes a genius to spot the obvious" - my old physics master

Brucey
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Re: not broken one of these before

Postby Brucey » 2 Oct 2020, 4:31pm

the replacement shimano models are BB-UN100 and BB-UN300.

They are built like SunRace and Chin Huar units, amongst others not noted for their longevity.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

drossall
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Re: not broken one of these before

Postby drossall » 2 Oct 2020, 6:25pm

Happened to me, although to be fair I don't recall whether it was a Shimano one or one of the similar Stronglight.

It wasn't too long after I started riding, decades ago, that I began to wonder how long it would be before I had broken every piece of a bicycle at one time or another...

Marcus Aurelius
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Re: not broken one of these before

Postby Marcus Aurelius » 2 Oct 2020, 7:17pm

If you use fishing equipment on a bike, this is what happens.

fatboy
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Re: not broken one of these before

Postby fatboy » 2 Oct 2020, 10:37pm

Brucey wrote:the replacement shimano models are BB-UN100 and BB-UN300.

They are built like SunRace and Chin Huar units, amongst others not noted for their longevity.

cheers


Why can't they leave well alone! Given the normal longevity of UN55 et al bottom brackets I've always had a suspicion that the external BB was to up sales of bearings :D
"Marriage is a wonderful invention; but then again so is the bicycle puncture repair kit." - Billy Connolly

Bonzo Banana
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Re: not broken one of these before

Postby Bonzo Banana » 3 Oct 2020, 4:44pm

Brucey wrote:the replacement shimano models are BB-UN100 and BB-UN300.

They are built like SunRace and Chin Huar units, amongst others not noted for their longevity.

cheers


Shimano do license out their brand for lower end stuff and outsource some production so wouldn't surprise me if they did that. I've just looked at the images of those 2 new bottom brackets. The UN100 is now made in China so could be outsourced but the UN300 is still made in Indonesia which I think is Shimano's own factory which has made bottom brackets for decades.

I have two experiences with Chin Haur bottom brackets. Many years ago I thought I'd got a bargain when I bought a brand new Kona Lanai half price at £150 which the seller had only had a short while which he paid £300 for and I won it at auction including delivery at £150. It was the worst Kona bike ever, garbage components (initially I thought the seller had swopped components but they were the standard spec). The Chin Haur bottom bracket constantly clicked and later found out there was a recall on them.

My second experience is I bought a Carrera Subway 8 from Halfords and on collection was told the bottom bracket had failed when they tested the bike so I got a free upgrade to a Shimano bottom bracket which I was very pleased about. More recently I saw a specification of the Subway 8 that I bought and it had a Chin Haur bottom bracket.

I find sunrace components ok, maybe about the same as lower end Shimano but I have no experience of their bottom brackets. I may be remembering wrongly but I had a FSA bottom bracket in one bike which was made in Taiwan and seemed very good.