Had a truativ Gxp bottom bracket fitted for probably about 500 miles and now the left hand (non drive side) is coming loose all the time. I tightened up the internal 8 mm bolt fairly tight last night and done less than 2 miles and the crack and pedal is almost falling off again. Any Ideas ? , New crank , BB or just a case of maybe not tightening the 10mm locking nut enough.
Ive got a spare shimano BB and can aquire a Hone crankset from a mate .

My friend has the same problem, they are Truvativ as well. I guess it is the bottom bracket and the threads have become worn down.

take the crank bolts out, dip them in some degreaser, dry them off and then put them back in again.

this comes up fairly regularly, common problem with the GXP, best solution is to remove BB and cranks and replace with shimano!

Yeah, I had the same problem, I tried loctite, new crank bolt, new crank to no benefit. In the end it turned out to be that I’d ripped some of the splines off the BB, as well as off the crank.
Have a look at your crank and BB see if there’s any obvious damage to the splines.

I’ve got exactly the same issue 🙁

I’ve run the same pair of Stylo cranks for 4 years hard use, replacing the external bb a few times during this time, without any isses whatsoever.

Recently I put in a new GXP BB (slightly different shape to the old one I took out, more rounded at the edges, but otherwise the same thing) and now the non drive side crank arm keeps working loose a few times every ride.

Splines which are attached to the drive side crank arm look fine, it just seems odd that this has started happening after replacing the BB with the new model.

It turns out the thread inside the drive was knackered as when I took it off and looked At the threads they were quite burred. Now got a shimano BB and old Hone cranks fitted and Its all good. I think I’ll stay away the Truvativ cranks and BB’s from now on.