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if frame constructed with a British manufactured shell there is a possibility you may find it to be slightly underwidth, ~66.5mm rather than the nominal 68mm

with such shells it is often helpful to place a one mm spacer behind fixed cup to achieve an ideal chainline, assuming frame in good alignment to begin with...

let readers know if you wish to stay with a cottered chainset or wish to change to cotterless so that their suggestions may be more on target

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