Need a little help...
 

OK here's the situation. It feels like there is a little skip when I'm pedaling. At first I thought it must be a stiff link in the chain, so I looked in to that and got no results. It happens always when my left pedal is at 6 o'clock, but only when I'm using the big ring. If I'm using the little ring everthing is smooth. I looked at the big ring for broken/bent teeth and couldn't find any so I'm totally lost. That is why I'm here asking you smart people. What is wrong with my bike?

Possibly you are feeling a rough spot in the pedal or bottom bracket bearings.

Have you checked it on a stand? If you can only feel it when you are on the bike, you might try checking to make sure your pedals or on tight. They may seem tight enough with a short wrench. You should remove them, lube the threads a bit, and really torque them up. I had a similar mystery and this worked for me. If you are only feeling it on the left pedal, start on that side.

The only reason it seems like you would feel it on the big wheel would be that you are applying more pressure to the pedal than you when you are on the granny.

I got some funny looks for this before, but I have seen it more than once.

If that is not it, next would be to check the bearings in the pedals and BB as recommended in the previous post.

Good luck.

- Jeff

Loose crankarm? Maybe the chain shifting around on a worn out chainring?