Loose cranks issue

Hi folks,

I'm hoping that someone here may be able to help.

Recently bought a RaceFace chainset on here, along with a new isis bottom bracket.
During the first ride, I noticed the l/h crank started to come loose :facepalm: Annoying, but I had an 8mm a/k with me and tightened it up. Really wanted to do a ride, so I carried on, and when I felt it loosening, I did it up again.
When I got home, I took the bolt out, cleaned the threads on the bolt and bb axle, before putting back on with threadlock. Followed by one of those self-extracting nuts that covers the outside of the 8mm bolt. Thought that would stop it, should it try to come undone again.
It happened again, loosening off, and the s/e nut was still tight on the crank. But this time I had a different set of allen keys. Up to 6mm! :roll:
It got so bad, that as I was stopping, the crank came away with my shoe!
Found out that my car ignition key fits! That did it up enough for me to get home. The tapers in the crank seems to be in good nick too. I'm at a loss to know how to stop this happening.

Any help in resolving this issue would be greatly received, thanks


Mike

Re:

Iteresting. Shoukdnt really happen on theser. Youved heck the crank is not bottoming out. Could be crank is worn, the crank and spindle are compatible?... im sure youve checked all this.

How tight are you doing up the bolt, you have torque wrench to check ((else a small spring scale and steel tube ver the allen key at set length)

Re:

The crank and bb are the same I think. Are there 2 types if ISIS bb? Bottoming out? You mean on the axle? If so, no it's not.
I'm away now so can't get pics 'til the weekend.
I don't have a torque wrench either, just do up to what I think is tight. What's even more confusing is the 8mm bolt undoing even with the extractor still tight! :? :facepalm:
Really don't want to get another bb and chainset,

HELP!

Mike

Re:

My ISIS Raceface cranks came loose first time out, non drive side arm same as yours. I tightened them up with a torque wrench and they've not come loose since. From what I remember the torque setting was pretty high, more than I would have done them up too with a 4" long Allen key even if I was properly leaning on it.

Where are you then? Wave!

47NM is quite a lot of torque. This is one of those instances where a torque wrench will quickly show you how wrong you are when you think something is tight enough. Shimano octalink cranks have a similar torque requirement. Whenever I work on a XTR BB I'm surprised on how much force I have to apply to get the cranks to factory spec. (some really hard pushing on a long handle torque wrench, not something you can achieve with a a hand-held 8mm Allen key).

Re:

In my experience, if a crank is ridden loose to the point of it coming off the axle, it will never again tighten up properly.

Though you might not be able to see it I suspect the tapers/splines are gubbed.

There is another type of ISIS BB, which is a Truvativ Howitzer (External bearing, ISIS spline).
The splines are the same as those on ISIS BB/cranks, but a different length so you can 'fit' a set of ISIS cranks onto a Howitzer BB, but they will never tighten up as there's not enough spline length to hold them.
It doesn't sound like that's what you've got, but the symptoms sound similar.

With ISIS BB/cranks I've had the same issues as some others too - loose & falling off, on 2 consecutive rides. The third one, I cleaned up all the splines (use no grease) and re-fitted with as much torque as I could muster and they never fell off again.

Re:

The one I have isn't an external bearing model. The bb was new, still sealed in the bag and the tapers in the cranks looked fine too.
As you say, I degreased the threads. I'll do the same with the splines I think and do it up ' bloody tight! '

Mike