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Drive-side Ultegra crank arm weirdness - is this dangerous or cosmetic?

by terrycojones
Tue, Dec 03, 2019 01:30
35

I was doing a hard uphill (virtual) ride last night with a lot of out-of-saddle riding. I noticed my right pedal felt increasingly odd and thought that the pedal might somehow be coming off. After the ride I had a look and found what's shown in the two pictures at http://jon.es/other/ultegra-crank-1.jpg and http://jon.es/other/ultegra-crank-2.jpg. What looked initially like just a cover was quite a bit further off than is shown in the images. At first I thought it was just a cosmetic thing and so I tapped (firmly) with a hammer on the 4 stubby arm-like sections that were coming away from the chain rings (the top-left arm in the 1st photo shows a pretty wide gap). They went back in to some degree, but as you can see in the photos that they're still not flush with the outer body of the rest of the front rings. But then I thought "hang on, if that's just a cosmetic cover, why did your pedalling start to feel so wonky & messed up?"  So now I'm guessing that that central 4-armed piece is actually integral to the whole ringset body and that maybe I'm in danger of having it completely break apart.

Has anyone experienced this before? It's Ultegra 6800, I believe. I've done over 20,000 km on it, so it's not exactly new. I changed the chain rings a few years back, but as far as I remember that didn't involve changing the part that now looks like it's about to break off / fall apart.

Thanks for any help / suggestions!

 

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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35 comments

Avatar
Thatsnotmyname | 4 years ago
0 likes

As others have said - the notion that this is related to use on a turbo is just nonsense.  Turbo use would not affect this, or any other crankset.

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brooksby replied to Thatsnotmyname | 4 years ago
0 likes

Thatsnotmyname wrote:

As others have said - the notion that this is related to use on a turbo is just nonsense.  Turbo use would not affect this, or any other crankset.

Why not? Isn't using a turbo almost the same thing as just riding the bike, and if it can happen when riding the bike, then...? 

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Thatsnotmyname replied to brooksby | 4 years ago
0 likes
brooksby wrote:

Thatsnotmyname wrote:

As others have said - the notion that this is related to use on a turbo is just nonsense.  Turbo use would not affect this, or any other crankset.

Why not? Isn't using a turbo almost the same thing as just riding the bike, and if it can happen when riding the bike, then...? 

Well, it could happen while on a turbo, but the turbo would still not be the root cause..

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Daveyraveygravey replied to Thatsnotmyname | 4 years ago
1 like

Thatsnotmyname wrote:
brooksby wrote:

Thatsnotmyname wrote:

As others have said - the notion that this is related to use on a turbo is just nonsense.  Turbo use would not affect this, or any other crankset.

Why not? Isn't using a turbo almost the same thing as just riding the bike, and if it can happen when riding the bike, then...? 

Well, it could happen while on a turbo, but the turbo would still not be the root cause..

 

...and the troll was saying it ONLY happens on a turbo, because the back wheel is fixed and can't move around like a bike would on the road kiss  It happens because pedals are turning crank arms, and some of these haven't been stuck together too well.

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Nick T | 4 years ago
0 likes

It's a failure at the point of chemical bonding between the two halves of the crank arm, and it's relatively well documented. The cause hasn't been established, it could be environmental such as using degreasers on the component, manufacturing fault, or "unsympathetic" use. I don't believe turbo use would exacerbate the problem, if anything it would prevent it - side loads are minimised when the bike is secured, Putting less strain on the adhesive than when leaning the bike heavily in a sprint for example 

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Thatsnotmyname | 4 years ago
0 likes

https://www.cyclechat.net/threads/turbo-trainer-hybrids.256356/
3
 

 

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Daveyraveygravey replied to Thatsnotmyname | 4 years ago
0 likes

Thatsnotmyname wrote:

https://www.cyclechat.net/threads/turbo-trainer-hybrids.256356/
3
 

 

 

What a tosser!  

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Daveyraveygravey | 4 years ago
0 likes

Yup, utter b/s

The website and my phone weren't getting on last night...

My bike has never been near a turbo, this is a pretty common fault.  I don't believe it is use on a turbo that is causing it; it may be making it happen more often, but I don't think that explanation makes sense.

OP, take the bike back to the shop you bought it from and start with them.  This could have had nasty consequences for you if it had let go when you were on a big effort, and it is not an acceptable failure.  The shop where I bought my bike from put me in touch with Madison, the UK distributor, and I eventually got a free replacement even though it was a year outside the warranty.

 

 

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Judge dreadful replied to Daveyraveygravey | 4 years ago
0 likes

Daveyraveygravey wrote:

Yup, utter b/s

The website and my phone weren't getting on last night...

My bike has never been near a turbo, this is a pretty common fault.  I don't believe it is use on a turbo that is causing it; it may be making it happen more often, but I don't think that explanation makes sense.

OP, take the bike back to the shop you bought it from and start with them.  This could have had nasty consequences for you if it had let go when you were on a big effort, and it is not an acceptable failure.  The shop where I bought my bike from put me in touch with Madison, the UK distributor, and I eventually got a free replacement even though it was a year outside the warranty.

 

 

Youre also wrong. The fault may ( and does ) occur on the road, putting the bike on the turbo helps it along nicely.

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Daveyraveygravey replied to Judge dreadful | 4 years ago
1 like

Judge dreadful wrote:

Daveyraveygravey wrote:

Yup, utter b/s

The website and my phone weren't getting on last night...

My bike has never been near a turbo, this is a pretty common fault.  I don't believe it is use on a turbo that is causing it; it may be making it happen more often, but I don't think that explanation makes sense.

OP, take the bike back to the shop you bought it from and start with them.  This could have had nasty consequences for you if it had let go when you were on a big effort, and it is not an acceptable failure.  The shop where I bought my bike from put me in touch with Madison, the UK distributor, and I eventually got a free replacement even though it was a year outside the warranty.

 

 

Youre also wrong. The fault may ( and does ) occur on the road, putting the bike on the turbo helps it along nicely.

 

How am I wrong?  My bike has NEVER been on a turbo.

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terrycojones | 4 years ago
0 likes

I have a Tacx Neo 2 Smart, which in theory does let you rock left/right - but maybe not enough.

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Vlad the Impailer | 4 years ago
2 likes

For those who cant afford a new rocking trainer....

 

Just build yourself a home made rocker plate to place your turbo trainer on top.

Takes a fiew pieces of timber / metal bar and a bit of DIY and 2 x inflatable 8" balls from amazon and youy have a rocker plate.

 

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IanEdward | 4 years ago
0 likes

Absolutely the opposite! My best bike resides on the turbo for half the year as I'm afraid to get it dirty/salty/drop it on icy roads.

By doing this I get all the training benefit of riding singlespeed commuters and 105 mudguard bikes for half the year, but will also probably get 5 years out of my Ultegra groupset and posh wheels. Truly Scottish parsimony!

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IanEdward | 4 years ago
1 like

Hmm... I wonderfed about the influence of the turbo! My 'good' bike spends 2/3rds of the year on the turbo due to good old Scottish weather.

It has Ultegra cranks as well. That being said, I rarely do any out of the saddle stuff on it, just seated.

*eyes two year old Ultegra cranks nervously...*

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Judge dreadful | 4 years ago
0 likes

You've got a problem caused by the abnormal torsion you exert on the cranks, when pushing hard, on a bike which can't move 'naturally' because it's stuck in a turbo. The lighter / better the cranks, the worse it gets. I'm seeing this sort of damage / issue more and more, as the popularity of turbo type riding increases. A rocking / dynamic tilt turbo, and / or rollers, are a better option.

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terrycojones replied to Judge dreadful | 4 years ago
0 likes

Judge dreadful wrote:

You've got a problem caused by the abnormal torsion you exert on the cranks, when pushing hard, on a bike which can't move 'naturally' because it's stuck in a turbo. The lighter / better the cranks, the worse it gets. I'm seeing this sort of damage / issue more and more, as the popularity of turbo type riding increases. A rocking / dynamic tilt turbo, and / or rollers, are a better option.

Ah... that makes complete sense, thanks. Maybe I should move to a more bulletproof  crankset, as changing turbo isn't feasible at this point. It will be interesting to see how things go with the replacement.

 

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srchar replied to Judge dreadful | 4 years ago
2 likes

Judge dreadful wrote:

You've got a problem caused by the abnormal torsion you exert on the cranks, when pushing hard, on a bike which can't move 'naturally' because it's stuck in a turbo. The lighter / better the cranks, the worse it gets. I'm seeing this sort of damage / issue more and more, as the popularity of turbo type riding increases. A rocking / dynamic tilt turbo, and / or rollers, are a better option.

Hang on - some people have Dura Ace... on their turbo bike?

I'm hardly the world's most parsimonious person, but that strikes me as being a tad extravagant!

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Drinfinity replied to Judge dreadful | 4 years ago
1 like

Judge dreadful wrote:

You've got a problem caused by the abnormal torsion you exert on the cranks, when pushing hard, on a bike which can't move 'naturally' because it's stuck in a turbo. The lighter / better the cranks, the worse it gets. I'm seeing this sort of damage / issue more and more, as the popularity of turbo type riding increases. A rocking / dynamic tilt turbo, and / or rollers, are a better option.

How is that the case? If you put force down on the pedal, yes, you are putting torque on the crank which is trying to twist it. However the proportion of that torque which would be relieved by accelerating the rotation of the bike towards the pedal if you were riding on road compared to a turbo is negligible- otherwise your power would go into spinning your bike onto its side.

I would agree that fixing a bike at the rear and putting the power down might make a difference at the seat stay, but not in the crank. 
 

The failure is an unacceptable defect, nothing to do with a turbo trainer.

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Judge dreadful replied to Drinfinity | 4 years ago
0 likes

Drinfinity wrote:

Judge dreadful wrote:

You've got a problem caused by the abnormal torsion you exert on the cranks, when pushing hard, on a bike which can't move 'naturally' because it's stuck in a turbo. The lighter / better the cranks, the worse it gets. I'm seeing this sort of damage / issue more and more, as the popularity of turbo type riding increases. A rocking / dynamic tilt turbo, and / or rollers, are a better option.

How is that the case? If you put force down on the pedal, yes, you are putting torque on the crank which is trying to twist it. However the proportion of that torque which would be relieved by accelerating the rotation of the bike towards the pedal if you were riding on road compared to a turbo is negligible- otherwise your power would go into spinning your bike onto its side.

I would agree that fixing a bike at the rear and putting the power down might make a difference at the seat stay, but not in the crank. 
 

The failure is an unacceptable defect, nothing to do with a turbo trainer.

 

you're wrong.

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ficklewhippet replied to Judge dreadful | 4 years ago
0 likes
Judge dreadful wrote:

You've got a problem caused by the abnormal torsion you exert on the cranks, when pushing hard, on a bike which can't move 'naturally' because it's stuck in a turbo. The lighter / better the cranks, the worse it gets. I'm seeing this sort of damage / issue more and more, as the popularity of turbo type riding increases. A rocking / dynamic tilt turbo, and / or rollers, are a better option.

Haha! Err, no.

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terrycojones | 4 years ago
0 likes

I took everything apart. Looks like this can be fixed relatively cheaply, via one of these https://www.ebay.co.uk/itm/Shimano-Ultegra-6800-170-mm-crank-arm-chainse...

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Hirsute replied to terrycojones | 4 years ago
0 likes
terrycojones wrote:

I took everything apart. Looks like this can be fixed relatively cheaply, via one of these https://www.ebay.co.uk/itm/Shimano-Ultegra-6800-170-mm-crank-arm-chainse...

Thanks, now I'm getting emails to buy this !!

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cjwebb | 4 years ago
3 likes

#wattagebazooka laugh

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terrycojones | 4 years ago
0 likes

Here's someone with the exact same issue https://youtu.be/kNHbEpQlMdE and here's someone else who had the problem and fixed it https://youtu.be/Vmp2G7zIby4.

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terrycojones | 4 years ago
1 like

I took a closer look. The chainring bolts are fine, and this is nowhere near them. The crank is just trashed, as people have suggested. I put my foot on the pedal and put a small amount of weight on it, and the gap between the spider and the crank rings just opens up. A bit more cycling the other day and the whole thing would have broken off. I stuck another picture online at http://jon.es/other/ultegra-crank-3.jpg which shows the extent of the gap when my foot (excuse the old ugg boot, sorry) is pushing down just a bit on the pedal.  Looking at it closely from the non-drive side with a flashlight, it's clear the spider is just breaking off. There are no nuts/bolts anywhere near - the bonded spider part and crank is just breaking away from the rest of the unit.  Time to buy a new one, it seems.

Thanks again for the help!

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terrycojones | 4 years ago
0 likes

Thanks everyone! I'm going to look to see if there are bolts I can tighten when I get home, but I'm not optiistic. From the various images I've seen online, this doesn't look like a bolt issue. I wonder how close I came to having the whole thing break off...

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srchar | 4 years ago
0 likes

See http://carlinthecyclist.com/shimano-dura-ace-fc-9000-crank-fail/

A totally unforgiveable failure mode.

Also see https://road.cc/content/forum/269221-chorus-chainset-175-52-36-avio-powe...

smiley

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Dingaling | 4 years ago
0 likes

Looks to me like the tabs on the ends of the crank arms that the chainring bolts pass through have sheared off. Never seen anything like it.

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terrycojones replied to Dingaling | 4 years ago
0 likes

Dingaling wrote:

Looks to me like the tabs on the ends of the crank arms that the chainring bolts pass through have sheared off. Never seen anything like it.

 

Yes, maybe so, though others say the spider bit is just somehow bonded/glued on. It would make more sense for the bolts to pass through it, of course. I'll take it apart so I can salvage the chainrings and will see. Thanks.

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huntswheelers | 4 years ago
1 like

Known fault and been doing the rounds in the Trade for a couple of years.... Dura Ace was the first to show early on now Ultegra cranks are failing .....

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