fixed drivetrain issue
about a month ago i bought a fuji track from my LBS and everything was going great until one day my cog slipped (or something like that, my friend said my lock ring needed to be tightened), so i took it in and the mechanic said it's normal for new bikes to have that problem. he fixed it up and it rode great, up until a few days ago when i felt like sprinting part of my commute. i started my sprint and i heard a creaking sound followed by a jerking of the drivetrain (it sounded catastrophic) but nothing more than the normal chain slack was to be felt when i slowed down (thankfully the fixed stayed fixed). i forgot about it and today my friend and i were on our way down the same open road, so i called out a flying sprint to the next light and we took off. as i powered away the same thing happened, but with more strange slipping or something. i'm going to take it in to my LBS tomorrow, but i figured in the meantime i'll post an inquiry here since i don't know how to diagnose the problem myself.
it's a stock 2009 fuji track, and i remember when i rode on a few different rental fuji track bikes at the encino velodrome when i was taking beginner classes over the summer, i could sprint without any strange problems like this, although i'm not sure if those bikes were stock or not...