On our tandem I just switched out a 175mm Truvativ Elita captain crank (old) for an FSA Gossamer 170mm (new). I reused/transferred the old crank bolts, and the new crank arms seemed to tighten completely and bottom out as they're supposed to. However, it seems that the outer dusk cap area of the new crank arms are shallower -- about 1-2 threads worth -- than on the old ones. Therefore the old crank bolts do not screw all the way in. They're close, but the outer part of the bolt caps do not fit flush and stick out about 2mm, and can spin.
My question: Is this only a cosmetic problem, or need I get slightly shorter and/or FSA-specific crank bolts?
Thanks for any thoughts or insight.