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You're right the issue was lack of torque, I have since bought a torque wrench.
The loctite is probably slight overkill but gives me peace of mind ;)
BTR88-
The loctite is probably slight overkill
It's not overkill, it's just plain wrong. The grease isn't there to make disassembly easier, it's there to make the assembly correct in the first place. Bolt torque gets converted into bolt tension, which converts to axial load on the crank, which pushes it up the inclined plane of the taper. There's a lot of friction on an inclined plane, and it's only by lubricating it that you can turn that push on the crank into the right amount of distance up the hill to create sufficient strain in the crank boss, which generates the hoop stress which provides the resistance to loosening by applying radial load at the interface. If the initial hoop stress is too low, the pressure between axle and crank will drop to zero on the low side when you start pedalling, and that's what lets the crank fall down the hill. Once that starts, it's then looser on the next turn and things start to fail catastrophically. A square taper is a pretty awful design, which is why you'd never see one on a machine designed after the invention of spline broaching tools except on a bicycle where legacy designs from the Victorian era remain current. Despite the problems, you can make a square taper into a reasonably reliable crank attachment if you understand the physics and give the kit its best chance of working.
gbj_tester
You'd have even less trouble if you used a spot of grease on the tapers, and if you do that and torque the crank bolt correctly they don't loosen.