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Crank fell off
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I hit a pot hole hard at the weekend, at the bottom of a hill, doing 55km/hr and my Ultegra crank arm came loose The plastic tension bolt had sheared off and one of the 5mm bolts was completely loose, the other was tight. I tightened it with an allen key, not super tight as I wasn't sure if I needed the tension bolt or not and it came loose again. Took it to my LBS, they had a look at the crank arm, said it looked fine and I got a new tension bolt. They ended up screwing it in for me. I took it for a quick ride round the block and it seemed OK. But I have an Ironman in 3 weeks.... I don't really want the crank arm coming off during the race. That will definitely be game over... I'm puzzled as to why it came off. Years of BMXing and MTBing, lots of punishment on the bikes and I've never had a crank do that. Any ideas why this could have happened? I installed the crank a few months ago, it was off my mates bike and near new. I'm reasonably OK with bike maintenance stuff, but perhaps I fucked this up? Not sure how though. LBS mechanic suggested I had not slid the crank arm on hard enough so it was almost flush with bottom bracket. I thought this would be impossible with the tension bolt? The only other thing is I didn't tighten the 5mm bolts enough, but that would be a bit retarded, although I can sometimes go full retard.




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Re: Crank fell off [zedzded] [ In reply to ]
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Was the crank arm retention pin in the correct position?
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Re: Crank fell off [jimatbeyond] [ In reply to ]
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jimatbeyond wrote:
Was the crank arm retention pin in the correct position?

Not sure. Have you got a pic? Is there a little nipple on the inside of the crank arm that slots into a hole on the crank axle?
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Re: Crank fell off [zedzded] [ In reply to ]
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zedzded wrote:
jimatbeyond wrote:
Was the crank arm retention pin in the correct position?

Not sure. Have you got a pic? Is there a little nipple on the inside of the crank arm that slots into a hole on the crank axle?

Yes,

There is a plastic piece (on the crank between the bolts) with a small metal pin.

Process is:

Slide crank arm on.

Tighten plastic crank retainer thingy hand tight or snug. This is your bearing pre load.

Push plastic piece with metal pin in. This is super obvious if done correctly/incorrectly.

Tighten crank bolts 12-14nm, basically you are OK to go to 14.

Maurice
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Re: Crank fell off [mauricemaher] [ In reply to ]
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mauricemaher wrote:
zedzded wrote:
jimatbeyond wrote:
Was the crank arm retention pin in the correct position?


Not sure. Have you got a pic? Is there a little nipple on the inside of the crank arm that slots into a hole on the crank axle?


Yes,

There is a plastic piece (on the crank between the bolts) with a small metal pin.

Process is:

Slide crank arm on.

Tighten plastic crank retainer thingy hand tight or snug. This is your bearing pre load.

Push plastic piece with metal pin in. This is super obvious if done correctly/incorrectly.

Tighten crank bolts 12-14nm, basically you are OK to go to 14.

Maurice

Gotcha! Thanks. I think I missed that bit....
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Re: Crank fell off [zedzded] [ In reply to ]
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I have had those fall off too, always do to my sloppy maintenance. Now I use a torque wrench and tighten one up until it clicks tighten the other one up until it clicks then go back to the first one and then back to the second one.

Sometimes riding with a loose crank will damage the left side crank arm you might want to consider grabbing a new one off of eBay given the amount you're paying to do that race.
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Re: Crank fell off [zedzded] [ In reply to ]
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As others mentioned, there is a “safety” piece so the arm will not fall off. You have to remove one of the pinch bolts and rotate it upward so the pin comes out of the hole in the bottom bracket so the arm can then slide off. Many people may remove this safety pin because they find it annoying when installing or removing cranks, but it serves the purpose to prevent the arm from coming off!

If you are worried, they do make a metal tension bolt. I cannot recall if it’s for an XTR mountain crank, or which Shimano crank, but you can ask the LBS and they can get you one. I do not like the plastic one either! Put some blue loctite on the pinch bolts and torque them to spec and you should be good! No worry!
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Re: Crank fell off [jharris] [ In reply to ]
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jharris wrote:
As others mentioned, there is a “safety” piece so the arm will not fall off. You have to remove one of the pinch bolts and rotate it upward so the pin comes out of the hole in the bottom bracket so the arm can then slide off. Many people may remove this safety pin because they find it annoying when installing or removing cranks, but it serves the purpose to prevent the arm from coming off!

If you are worried, they do make a metal tension bolt. I cannot recall if it’s for an XTR mountain crank, or which Shimano crank, but you can ask the LBS and they can get you one. I do not like the plastic one either! Put some blue loctite on the pinch bolts and torque them to spec and you should be good! No worry!

OK. So from what I understand the tension bolt isn't under load hence the reason it's made of plastic, but in case something goes wrong a metal bolt will hold it together as opposed to snapping like mine did?
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Re: Crank fell off [zedzded] [ In reply to ]
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zedzded wrote:
jharris wrote:
As others mentioned, there is a “safety” piece so the arm will not fall off. You have to remove one of the pinch bolts and rotate it upward so the pin comes out of the hole in the bottom bracket so the arm can then slide off. Many people may remove this safety pin because they find it annoying when installing or removing cranks, but it serves the purpose to prevent the arm from coming off!

If you are worried, they do make a metal tension bolt. I cannot recall if it’s for an XTR mountain crank, or which Shimano crank, but you can ask the LBS and they can get you one. I do not like the plastic one either! Put some blue loctite on the pinch bolts and torque them to spec and you should be good! No worry!


OK. So from what I understand the tension bolt isn't under load hence the reason it's made of plastic, but in case something goes wrong a metal bolt will hold it together as opposed to snapping like mine did?

Much like the "lawyer" tabs on your front forks, the insert that goes between the two bolts is designed to prevent exactly this from happening. This plastic part is for preload adjustment basically....
How is the prep going for IMWA?? Less than 3 weeks until race day now!
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Re: Crank fell off [Amnesia] [ In reply to ]
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Amnesia wrote:
zedzded wrote:
jharris wrote:
As others mentioned, there is a “safety” piece so the arm will not fall off. You have to remove one of the pinch bolts and rotate it upward so the pin comes out of the hole in the bottom bracket so the arm can then slide off. Many people may remove this safety pin because they find it annoying when installing or removing cranks, but it serves the purpose to prevent the arm from coming off!

If you are worried, they do make a metal tension bolt. I cannot recall if it’s for an XTR mountain crank, or which Shimano crank, but you can ask the LBS and they can get you one. I do not like the plastic one either! Put some blue loctite on the pinch bolts and torque them to spec and you should be good! No worry!


OK. So from what I understand the tension bolt isn't under load hence the reason it's made of plastic, but in case something goes wrong a metal bolt will hold it together as opposed to snapping like mine did?


Much like the "lawyer" tabs on your front forks, the insert that goes between the two bolts is designed to prevent exactly this from happening. This plastic part is for preload adjustment basically....
How is the prep going for IMWA?? Less than 3 weeks until race day now!

Well it was going well until bits started falling off my bike!
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