Hi. you just have to be very careful. make sure the clamp bolt is as loose as possible or even remove it. on some models of TTT and Modolo stems there was a small allen bolt to help open the clamp a bit more. if you need to take a big screwdrive and spread the clamp just a bit to get it over the center of the bars. after that it should slip off easily. usually a bit of scuffing in the curves is not a big deal as it it usually covered by tape.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk