We changed to a longer set of cranks (same make), and have tightened the crank as tight as it will go without stripping. There is still a space of approx 2mm between the crank and the lip on the bottom bracket (can't remember whether that gap was there when we took it off. ) But now the front derailleur won't change onto the largest gear, and the adjustment is at its max. We cannot tighten the bottom bracket either. Any ideas, please?
The new crankset is not exactly in the same position as the old one, so you need to adjust the front derailleur. The internet is full of instructions for the procedure, so I am not writing a new guide here.