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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

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Miller | 5 years ago
2 likes

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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Daveyraveygravey | 5 years ago
2 likes

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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Freddy56 | 5 years ago
7 likes

It has only Virtually come loose. it didnt really happen

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kil0ran | 5 years 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 replied to kil0ran | 5 years ago
0 likes

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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