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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!

 

25 comments

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kil0ran [1760 posts] 3 days ago
2 likes

I'd imagine that your chainring bolts have worked loose. Have a look from the non-drive side. They're torx head bolts (T25 I think, possibly T30). You can tighten them with a long driver from that side without removing the cranks. In my experience with 5800 they tend to work loose over time and are a source of difficult-to-find ticking noises under heavy load. Tend to check mine once a month and inevitably at least one is slightly loose. Would definitely result in the behaviour you experienced if more than two were loose - and like any bolted system once one bolt is loose the others start to loosen up too.

Exploded view here shows how it all screws together

https://si.shimano.com/pdfs/ev/EV-FC-6800-3609A.pdf

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terrycojones [45 posts] 3 days ago
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kil0ran wrote:

I'd imagine that your chainring bolts have worked loose.

 

Ah... yes, that makes perfect sense! I will take a look tonight. Thanks a lot  1

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Freddy56 [441 posts] 3 days ago
6 likes

It has only Virtually come loose. it didnt really happen

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Daveyraveygravey [712 posts] 3 days ago
1 like

Happened to me about a year ago, it's broken.  The two parts should be bonded together; I had had mine about 3 years and there is a 2 year warranty.  Shimano originally tried to get out of it but I kept the pressure on them and they eventually replaced it under warranty.  I had been on a mission to climb Rosedale Chimney  in Yorkshire, the bloody thing let me get to within about a mile before I realised it was a potential disaster.  Glad it didn't happen when I was out the saddle on the climb!  It was something like a 25 mile ride back to base, rolling and then praying when I had to pedal it would hold together.

Lots of info on google about, here's a thread on bike radar - https://forum.bikeradar.com/discussion/13064693/ultegra-crank-failure/p3

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Miller [306 posts] 3 days ago
1 like

Yep, it's utterly borked. As mentioned above there's tons of discussion on the internet about this thing happening to D-A and Ultegra chainsets. These chainsets are made in two halves that are bonded (glued) together. Yours just fell to bits.

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huntswheelers [187 posts] 3 days ago
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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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Dingaling [134 posts] 3 days ago
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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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srchar [1658 posts] 3 days ago
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terrycojones [45 posts] 3 days ago
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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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terrycojones [45 posts] 3 days 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 [45 posts] 3 days ago
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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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terrycojones [45 posts] 3 days ago
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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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cjwebb [54 posts] 3 days ago
2 likes

#wattagebazooka laugh

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terrycojones [45 posts] 3 days 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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Judge dreadful [444 posts] 2 days ago
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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 [45 posts] 2 days ago
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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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IanEdward [384 posts] 2 days 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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srchar [1658 posts] 2 days ago
3 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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IanEdward [384 posts] 2 days ago
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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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Vlad the Impailer [35 posts] 2 days 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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terrycojones [45 posts] 2 days ago
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I have a Tacx Neo 2 Smart, which in theory does let you rock left/right - but maybe not enough.

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Drinfinity [279 posts] 2 days ago
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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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ficklewhippet [114 posts] 2 days 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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Daveyraveygravey [712 posts] 1 day 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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hirsute [1252 posts] 1 day ago
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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 !!