Dura Ace large chain ring lateral failure

[Adam Finn]

            Dura Ace 9000 compact crank set (2016 done 12000km)
Large chain ring collapsed inwards/sideways behind crank.
Never heard of this happening before.
Noticed a slight wobble early in the ride - suddenly collapsed when put under strain at end of a descent - overlapping the small chain ring and so rendering the bike unrideable.
The metal covers either side of the large ring got bent and somewhat distorted.
Question is: is this just a matter of replacing the chain ring or does the damage to the covers mean a whole new crank set?
Thanks!
Adam
PS Struggling a bit to attach photos - hope it worked!

[Jesper]

(08-23-2022, 04:49 AM)Adam Finn Wrote:  Dura Ace 9000 compact crank set (2016 done 12000km)
Large chain ring collapsed inwards/sideways behind crank.
Never heard of this happening before.
Noticed a slight wobble early in the ride - suddenly collapsed when put under strain at end of a descent - overlapping the small chain ring and so rendering the bike unrideable.
The metal covers either side of the large ring got bent and somewhat distorted.
Question is: is this just a matter of replacing the chain ring or does the damage to the covers mean a whole new crank set?
Thanks!
Adam
PS Struggling a bit to attach photos - hope it worked!

If the cover is simply pressed onto the crank then maybe you can get just that part while replacing the ring; I'm not familiar with that Shimano set-up.

I have seen rings collapse before, usually under the load of climbing while out of the saddle and using the large ring in front, and the largest or a large cog on the rear ("cross-chained"). Somewhat more common in the age of "drillium" when some riders took the removal of "excess" material to reduce weight to an extreme, and ended weakening a component to a dangerous level where the integrity of the part could be called into question if used under heavy loads.

What rear gear were you riding in when it happened?

It depends on where your chainline is when you are in a specific front ring. I tend to bias my chainline towards the outer rear cog more than centered on the the rear cluster (referenced inline centered between the front rings) due to my cycling habits/style.

If you have changed your bottom bracket (and used a different length, and/ or changed cranks, then your chainline may be different from what is was when stock. If you changed rear gear capacity that might also change your chainline depending on how the wheel is dished.

[Adam Finn]

(08-23-2022, 08:27 PM)Jesper Wrote:  

(08-23-2022, 04:49 AM)Adam Finn Wrote:  Dura Ace 9000 compact crank set (2016 done 12000km)
Large chain ring collapsed inwards/sideways behind crank.
Never heard of this happening before.
Noticed a slight wobble early in the ride - suddenly collapsed when put under strain at end of a descent - overlapping the small chain ring and so rendering the bike unrideable.
The metal covers either side of the large ring got bent and somewhat distorted.
Question is: is this just a matter of replacing the chain ring or does the damage to the covers mean a whole new crank set?
Thanks!
Adam
PS Struggling a bit to attach photos - hope it worked!

If the cover is simply pressed onto the crank then maybe you can get just that part while replacing the ring; I'm not familiar with that Shimano set-up.

I have seen rings collapse before, usually under the load of climbing while out of the saddle and using the large ring in front, and the largest or a large cog on the rear ("cross-chained"). What rear gear were you riding in when it happened?
It depends on where your chainline is when you are in a specific front ring. I tend to bias my chainline towards the outer rear cog more than centered on the the rear cluster (referenced inline centered between the front rings) due to my cycling habits/style.
If you have changed your bottom bracket (and used a different length, and/ or changed cranks, then your chainline may be different from what is was when stock. If you changed rear gear capacity that might also change your chainline depending on how the wheel is dished.

Thanks Jesper - interesting. I was definitely on the big ring when it happened but not cross-chained. I'd noticed an asymmetry in the rotation of the chain ring earlier in the ride - so I'm guess it was already damaged perhaps by a previous cross-chained event. A

[ReapThaWhirlwind]

It looked like it was ready to go.

They don't last forever. Remember that all friction adds in the wearing of components, so bad maintenance can also be to blame whenever a component fails. Not cleaning, not lubricating, not changing the grease, not changing the BB, etc.

[enkei]

That looks like yet another Shimano Hollowtech failure. It's a common problem and has been known about for many years. It's particularly prevalent in hot/humid places or if you regularly ride in the rain (as least, that's my understanding).

I think it's usually caused by galvanic corrosion (between the two halves of the hollow spider, which are glued together) and there's no way to repair the crankset. Sorry to be the bearer of bad news.

If you Google "Shimano Hollowtech failure" you'll find a bunch of stuff to read/watch.