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

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  • December 3, 2019 at 1:30 am #30314
    terrycojones

    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!

     

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  • December 4, 2019 at 1:43 pm #953479
    0
    Vlad the Impailer

    For those who cant afford a

    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.

     

    December 4, 2019 at 10:53 am #953477
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    IanEdward

    Absolutely the opposite! My
    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!

    December 4, 2019 at 10:27 am #953475
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    srchar
    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!

    December 4, 2019 at 9:28 am #953473
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    IanEdward

    Hmm… I wondered about the
    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…*

    December 4, 2019 at 9:19 am #953471
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    terrycojones
    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.

     

    December 4, 2019 at 8:37 am #953469
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    Judge dreadful

    You’ve got a problem caused

    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.

    December 3, 2019 at 11:06 pm #953467
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    terrycojones

    I took everything apart.

    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-chainset-NEW/264543368875

    December 3, 2019 at 7:27 pm #953465
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    cjwebb

    #wattagebazooka 

    #wattagebazooka laugh

    December 3, 2019 at 7:16 pm #953463
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    terrycojones

    Here’s someone with the exact

    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.

    December 3, 2019 at 7:04 pm #953461
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    terrycojones
    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.

    December 3, 2019 at 6:55 pm #953459
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    terrycojones

    I took a closer look. The

    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!

    December 3, 2019 at 4:37 pm #953457
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    terrycojones

    Thanks everyone! I’m going to

    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…

    December 3, 2019 at 4:02 pm #953455
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    srchar

    See http://carlinthecyclist

    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-power-meter-ps175

    smiley

    December 3, 2019 at 2:12 pm #953453
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    Dingaling

    Looks to me like the tabs on

    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.

    December 3, 2019 at 2:01 pm #953451
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    huntswheelers

    Known fault and been doing

    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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