[QUOTE=HillRider;9495868]

If it's a "square taper" crank and you rode it while it was loose, you may have damaged the crank to the point where it will never stay tight again.

/QUOTE]

Hi

That sounds like my problem with my daughters bike, pedal comes loose and the centre nut holding it in place loosens too. Tightened it a few times, but the same thing happens.
On inspecting the bolt, the first quarter of the thread is stripped. Maybe a new bolt will solve the problem.

G