I think that the problem with the clutch centre, is that the spline length is only 1/4" and only about 3/16" engage on the shaft. improvement can be made by replacing the thick washer (one thick one thin either side of the rollers, chainwheel bearing) the inside one, for the thiner one. ie. two thin washers: I improved mine further, by using the thick washer but counter boring it and machining the back of the clutch centre to suit, I now have a full 1/4" engagement of the splines. With regaurds to locking the nut, it can be tapped and a grub screw used to tighten against the clutch centre. The now supplied nuts are larger (mine 32mm across flats) allowing this to be done. Although, I have only used thread lock.