Shimano crank arm fell off mid-ride on Tuesday

I was about 8 miles into a morning ride on the Greenway trail when my left pedal started feeling loose. Before I could even stop, the whole crank arm just dropped off. Turns out the self-extracting bolt had backed out completely over time. I had to walk 2 miles to the nearest bike shop in my cleats carrying the crank arm. The guy at the shop said he sees this at least once a month, especially on bikes that get ridden in wet conditions. I should have checked that bolt during my weekly cleaning. Now I put a tiny drop of blue threadlocker on it and torque it to spec. Has anyone else had a crank arm fail on them like this? What do you do to keep yours from backing out?

2 comments

2 Comments

grantl941d ago

My neighbor had his Ultegra crank let go at hour 50 of a 200 mile endurance race. The real problem nobody talks about is how the newer hollow crank arms flex more than the old solid ones, which can actually work the bolt loose faster over time. I stopped relying on just threadlocker and started marking the bolt head with a silver paint pen after torquing it. That way I can glance down and see instantly if it has moved even a little bit since my last ride. Been doing that for about two years now and haven't had a single issue, even after riding through some pretty nasty rain storms.

ruby56122h ago

Dude, nothing says "trust your equipment" like a crank arm deciding to peace out 150 miles from anywhere. Sounds like your neighbor had a real "get to know your local flora" moment while walking back. @grantl94, that paint pen trick is absolute genius for anyone who's ever had that sinking feeling of "wait, did I torque that thing or just think really hard about it?" My paranoid method is just staring at the bolt while holding a flashlight like I'm interrogating it, so your way seems way more reliable. Plus it doubles as a tiny art project on your bike, which is a nice bonus for all that anxiety.

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