For the past two weeks or so, I've been experiencing a "clunk" sound from the crank / BB area of my '07 Giant Bowery (fixed gear). The cranks and BB are completely stock, and I've only had the bike for a few months, so common sense tells me that the problem can't be attributed to wear and/or improper installation of aftermarket parts.
The noise occurs each time I put moderate-heavy downward force on the cranks (both left and right) while in a sprinting-type riding mode. The clunk is also detectable through my feet. It almost feels as if something in the BB is slipping and catching itself after a small ammount of crank revolution.
Any help is much appreciated. Feel free to ask questions. Thanks!
You've probably just got a loose BB cup. Worst case, your BB is a dud and you should bring it in to warranty it. Also, make sure your crankarms are tight...if not, you'll be seriously lucky if it/they are still usable.
you'll want to tighten the cog on the hub as much as possible before tightening the lock ring -- if you have a chain whip you can use that, or go find a steep hill and jam on the pedals as hard as you can (don't put any back pressure on the pedals otherwise you'll unscrew the cog, which is probably what has been happening). then use a lock ring tool to tighten the lock ring down onto the cog, remember that it's reverse threaded. your lbs might help you out for free if you don't have the tools...
You may have some moisture in the BB. As strang as this sounds, I have found this to be a problem before. You will need to remover the BB and then dry the inside of hte frame area. When you reinstall the BB put teflon pipe on the threads.