i upgraded my dahon boardwalk crankset to a Shimano 105 54/39T chainring. it wasn't the easiest job as i have to resort to using my auto tools instead of the bike tools. the BB of my Dahon Boardwalk D7 is the cheap one that has unusual treading. i have to used my long nose plier coupled with adjustable wrench. while sticking the 2 ends of the plier to the notches of the bottom bracket, i have to crank it with an adjustable wrench. it took me more than an hour just to remove the BB bracket. once they're out it's pretty much an easy install of Hollowtech II BB and the 105 crankset (i attached a pic). now here's my problem. when on the 53T the gear shifting is ok but when i changed it to the 39T the chain slacks. it seems that the chain is too long. how can i fix this ?
thanks for the inputs,