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Crank fell off

 
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iwaters




Joined: 06 Sep 2016
Posts: 226

PostPosted: Wed May 24, 2017 10:53 am    Post subject: Crank fell off Reply with quote

I last used my Tri bike last September, just before I used it at an Oly I swapped the crank (it had a compact I switched to 53/39 as I was doing a very flat course). I think when installing it I made a boo boo.

Fast forward to last night. I was in a rush and got the Tri bike out, pumped the tires up and set off, without tools!

30 mins in and the left crank arm fell off (Ultegra Hollotech II). Thankfully a kind passer by lent me an allen key.

Anyway do we think the crank is fubard? I am guessing I didn't tighten the nuts equally. If thats the case then I suspect it has rounded the splines, possibly it just worked lose.

I have a race next weekend and don't want it to happen then. I guess tighten it up and try it a couple of times before hand and see?
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Chrace




Joined: 28 Apr 2010
Posts: 2517
Location: Eating a Yorkie

PostPosted: Wed May 24, 2017 11:15 am    Post subject: Reply with quote

Doesn't sound like it was on properly from the off.

The HT2 has a lock thingie (l/h side) that should stop it from falling off, although the main purpose is to ensure that the crank is on enough to bite. If that hasn't been clicked the crank wouldn't have been on proper.

Is it 12-14Nm or something for Ultegra or do I remember wrong? Did you tighten with a torque wrench or just on feel? It can take quite some tightening force without damage...
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iwaters




Joined: 06 Sep 2016
Posts: 226

PostPosted: Wed May 24, 2017 1:12 pm    Post subject: Reply with quote

Yeah its about 12-14nm, I have a torque wrench but cannot remember if I used t when I did that. You are supposed to screw the pre load in first then tighten to two bolts equally.

I haven't done one of those things properly clearly. I will inspect the splines and see if they are rounded off.
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Chrace




Joined: 28 Apr 2010
Posts: 2517
Location: Eating a Yorkie

PostPosted: Wed May 24, 2017 3:51 pm    Post subject: Reply with quote

If the splines are rounded I thought you would have felt it slipping or clicking on each rotation. Your pedal force is mainly rotational so for it to slide out sideways so far it could fall off must have been quite something.

Puzzled. Smile
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Tin Pot




Joined: 08 Jul 2013
Posts: 2196
Location: Bromley

PostPosted: Wed May 24, 2017 9:30 pm    Post subject: Reply with quote

Chrace wrote:
Doesn't sound like it was on properly from the off.

The HT2 has a lock thingie (l/h side) that should stop it from falling off, although the main purpose is to ensure that the crank is on enough to bite. If that hasn't been clicked the crank wouldn't have been on proper.

Is it 12-14Nm or something for Ultegra or do I remember wrong? Did you tighten with a torque wrench or just on feel? It can take quite some tightening force without damage...


+1

Although my crank fell off a few times then the spline went and I replaced the whole crankset. So it could indicate wear, but you'll find out in due course.
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iwaters




Joined: 06 Sep 2016
Posts: 226

PostPosted: Thu May 25, 2017 11:49 am    Post subject: Reply with quote

Yeah I a am hoping the nuts just worked lose and it fell off. You are supposed to re torque them after 80km and I hadn't done that.

Will look at it on the weekend. Just want to make sure it doesn't fall off in the race.
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kevb




Joined: 11 Aug 2010
Posts: 762

PostPosted: Thu May 25, 2017 7:58 pm    Post subject: Reply with quote

Do you have the plastic 'bolt' installed in the end of the axle spindle? I forgot to tighten the allen bolts on one one and it was a bit wobbly but didn't feel it was in danger of falling off. most of mine have lost the plate pin, and haven't had any problems (yet!).
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iwaters




Joined: 06 Sep 2016
Posts: 226

PostPosted: Sun May 28, 2017 10:07 am    Post subject: Reply with quote

The spines all look fine. I've re-seated it and properly torqued it. Will try a couple of rides and re-torque before the race and hopefully it will be ok.
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