Non drive side crank bolts keep coming loose.

[SIZE= medium]Hi All[/SIZE]

[SIZE= medium]First of all, thanks for looking at my thread![/SIZE]

[SIZE= medium]I have a Specialised Allez double with a bum-basic tapered BB; the left crank bolt keeps coming loose.[/SIZE]
[SIZE= medium]I have taken it off and inspected it closely, I can’t see that the tapers in the crank arm have rounded off, and the BB itself seems to be in good overall condition.[/SIZE]

[SIZE= medium]What could possibly be the problem?[/SIZE]

 

A couple of questions: how long have you had this BB and the crank arms that are with it? Have you changed either the crank arms or the BB? Are you putting grease between the crank arms and the tapered ends of the BB axle?

 

Hi

They are OEM parts from new - I have clocked up just under 2k miles on them.
I have tried with and without grease, I have also tried purple thread lock on them.

 

If the crank bolt does not currently have a WASHER, then add one ...

• one which you can CUT one from a milk jug bottle cap will probably work

If the bolt has a washer, then get a SPLIT or STAR WASHER (you will probably need to go to an automotive supply store for the latter) ...

BTW. Are you saying that the crank arm, itself, is not coming loose ... BUT, that the bolt, alone, is loosening ... OR, is the bolt coming loose & the crank arm subsequently coming loose?

If the crank arm is coming loose, too, then you probably need to shim it ...

• a fold of some THIN brass stock (or, equivalently thin METAL stock) shrouding two sides of the taper will probably work.

 

[SIZE= 10pt]What appears to happen, after about 3 miles of riding the crank nut loosens, then the crank arms starts to make
a very annoying squeaking noise.[/SIZE]

[SIZE= 10pt]Once you tighten the bolt the noise goes away, the crank arm doesn’t appear to be perceptibly loose, although it must be as the noise is coming from the crank arm and BB.
I'll give what you said a try and add a little washer.[/SIZE]

 

If the bolt tightens too easily or draws the crank arm very close to the bearing cup the crank arm is probably worn from repeated removal/installation and you may have to use Alf's shim idea. I would try the brass shims between crank arm and spindle before trying the second bolt washer since the arm has loosened (and possibly deformed/worked away material).

Clean the internal and external threads with acetone prior to using any thread locking adhesive. If purple is letting go, switch to red Loctite. It's still a non-permanent locker that will require higher removal torque and possibly a little heat.

 

Agree that it's likely your crankarm has stretched or yielded. When you tighten the bolt, you should feel and see the arm being forced further onto the taper as the bolt gradually reaches the specified torque. If the crankarm isn't moving and the bolt is easy to turn until the last revolution or so, that would indicate your crankarm is permanently stretched. Comparing the fit of the left side to the drive side crankarm may also confirm this condition.