The non-drive side of my external bottom bracket Truvativ cranks has developed a habit of falling off. They are second hand, but new to me, so I've no way of knowing whether they've always done it, but since Thursday morning they've done it every 10 miles or so. The splines are a bit roughed up, but they do back up alright.

With a square taper, once the crank had fallen off once that was pretty much game over, but with externals surely it shouldn't be quite as critical as there's a big bolt actually holding the crank in place. Or am I being optimistic, will movement in the splines between the crank and the axle inevitably loosen the bolt? Any thoughts?

I've dismantled, de-greased and threadlocked to hell for the moment. 🙁

I've had loads of bikes back with Turdativ cranks falling off for no apparent reason. Once it comes loose it will never stay on. No amount of ridiculous torque on the bolt will keep them on. Strangely they are never covered under warranty by the importer.

Buy a new crank arm or by some new cranks entirely if I were you.

That all sounds depressingly plausible, cheers.

Same here. I especially enjoyed riding twelve miles home stopping every 50 yards to tighten up the bolt using two 4mm allen keys side by side to make an 8.

I eventually gave up on truvativ and bought shimano. never had a problem since. (But still always carry an 8mm key…)

i have some gxp (external bb) stylo cranks that the non driveside arm used to come loose, i just lock tight it on now and carry an 8mm with me, be careful tightening the crank bolt i have snapped one all to easily.

Same here, lots of lock tight and always carry an 8mm allen key.

Won't be buying any again

I would try some loctite on the splines of the axle and the threads of the bolt. Easy on the threadlock on the bolt cos its easy to get the bolt stuck and round it when the time comes to get them off, but you can always tap the crank arm off with a hammer.

I use the red studlock or bearing fit stuff thats a bit stronger than the normal stuff.

I've had this problem with Raceface cranks, the spline interface loosens over time and presto, you have wobbly cranks.

Won't be buying Raceface again any time soon…

I am happy to report that I took against the bugger last night, slathered it in No More Nails and tightened it up until the stuff oozed out everywhere. Then I carried an 8mm allen key. Got to work without it coming loose, and will check before I set off home.

What was the problem with square taper again? Something to do with the crank interface coming loose if I remember rightly… 🙂

What was the problem with square taper again?

Apparently roadies on drug were breaking it. Oh and the obvious need for more marketing crap 😉