Why would this come loose?

[Bajs]

I was out a cycle today and the part i am pointing to in the photo popped out, i managed to tighten it back up and cycle home but i dont know how or why this part would come loose! Surely it cant unscrew through pedalling cause that would be pointless! Can anyone help me out?

 

[black'n'yellow]

if the crank pinch bolts are not tight enough, the cap may loosen - worth checking them.

 

[MontyVeda]

crank bolts do have a habit of coming loose if they're not done up ba$tard tight... a long handled allen key helps.

 

[Bajs]

Cheers folks, ill get an allen key in there and tighten it untill blood draws!

 

[ianrauk]

You don't need to tighten up the cap too much. Just nip it tight. It's just to preload the bearings

 

[Dave Davenport]

crank bolts do have a habit of coming loose if they're not done up ba$tard tight... a long handled allen key helps.

Err... it's not a crank bolt.

 

[ianrauk]

Err... it's not a crank bolt.

Read his post in the context of Black 'n' Yellow's.

 

[MontyVeda]

I am certified blonde y'know!

 

[BimblingBee]

Doing pinch bolts up tight enough so you draw blood is a sure fire way of stripping alloy threads! You don't need to go nuts.

 

[simon.r]

Technically I think* I'm right in saying you don't need that bit after you've installed the cranks (much like the cap on a Ahead-set).

*I may be thinking wrong as my experience of 'modern' cranks is limited. Still think there's nowt wrong with square taper

P.S. Did anyone mention a torque wrench yet?

 

[black'n'yellow]

Technically I think* I'm right in saying you don't need that bit after you've installed the cranks (much like the cap on a Ahead-set).

except that tightening the pinch bolts on the crank usually clamps the end cap in place.

 

[Cubist]

Make sure when tightening them that you do it a quarter turn each in turn. Tightening one bastard tight while the other is slack is a sure fire way to shear the end of the crank.

 

[Bajs]

Thanks for all the help folks, hopefully thats it sorted now!