Anyone know why this keeps coming undone?

[gaz]

The thing on the end of the crank, I tighten it up but it keeps coming undone :/

 

[tyred]

What thing is this?

But anyway, you may have damaged threads. Try some Loctite thread locking compound.

 

[ianrauk]

Because it hadn't been tightened enough.
You need to loosen the two crank bolts.
Tighten up the nut. Or I should say nip it up as it's to tension the bearings so it shouldn't be too tight.
Then do the two bolts back up.

 

[gaz]

Because it hadn't been tightened enough.
You need to loosen the two crank bolts.
Tighten up the nut. Or I should say nip it up as it's to tension the bearings so it shouldn't be too tight.
Then do the two bolts back up.

So that's my problem, I need to undo the other bolts first. Thanks
I feel like i'm doing it up enough, although I don't have a torque wrench that goes as low as 1.5Nm

 

[subaqua]

thats just a bit over finger tight .

there are a few levels of tightness

finger tight
Nipped up
FT
W#'';'d up hard

most on a bike are Nipped up.

this is for steel OR Alu .

carbon bikes are a different matter and one should spend the GDP of a minor african nation on a torquewrench that reads proper low.


the above guide is for entertainment only and if any hamfisted spanner manglers are reading don't do it go and buy a torque wrench

 

[Flying Dodo]

In my experience, FSA cranks have an issue with the pre load bolt coming loose. I ended up ditching them because of that. Shame, as they were lovely carbon ones.

 

[lpretro1]

The 'thingy' is the pre-load bolt for the bearings. This must only be done up finger tight - the proper tool usually is plastic one to stop you overtightening it. Once that is done up you push the little tab back down and then torque the two allen bolts to 12-14nm.

 

[Smurfy]

Isn't it the case that this component serves no purpose once the two clamp bolts are tightened. Same as the Aheadset pre-load bolt isn't it? If that's true then in theory you could just take it out and put it in your tool bag.

If you don't like the 'look' with it missing, you could remove it after tightening the clamp bolts, then wrap one revolution of plumbers PTFE tape around the threads. PTFE tape is very soft*, so will squash right down when you reinsert the bolt, but hopefully with just enough friction and rattle-resistance to stay put. If it still comes loose, put two revolutions of tape around the threads, and so on.


* Don't buy natural gas PTFE tape. It's much more dense/hard, and costs a lot, lot more.

 

[gaz]

The 'thingy' is the pre-load bolt for the bearings. This must only be done up finger tight - the proper tool usually is plastic one to stop you overtightening it. Once that is done up you push the little tab back down and then torque the two allen bolts to 12-14nm.

as it's an FSA it takes a hex key rather than that crappy shimano plastic thing, but same principle otherwise I guess. Ta

 

[Cubist]

Threadlock it, or remove it for safekeeping. One you've loaded the bearings and nipped up the opposing crank pinchbolts it's superfluous.

 

[gaz]

Hmmm. it keeps coming undone and literally nearly falling out after 20miles.
As per cubists post, I'll try some threadlock on it just to keep it in place.

 

[ianrauk]

Hmmm. it keeps coming undone and literally nearly falling out after 20miles.
As per cubists post, I'll try some threadlock on it just to keep it in place.

Or some PTFE tape.

 

[VamP]

It's a design flaw on the FSA cranks. Threadlock will sort it, but as the low end FSA cranks are pretty flexi, I ended ditching mine after a few months. PITA. I avoid them like the plague now.

 

[GrumpyGregry]

remind me, for mere mortals, what was wrong with square taper bottom brackets?

 

[VamP]

remind me, for mere mortals, what was wrong with square taper bottom brackets?

They're from the past.