Hello All,

I am new to road biking and just picked up a 1987 Cannondale SR500. The bike has been a blast to ride so far. I got the bike tuned up recently but noticed that at certain positions on the crank rotation the crain was rubbing the front derailleur. I took it back to the mechanic and he/we discovered that the chain was actually moving on rotation some. I did some more investigating myself by removing the chainrings (which seem very flat). But then found that the problem seems to be the spider crank. Here is a youtube video of my findings (notice how at some points it doesn't contact the arm but at others it rubs a lot.)

Bent crank? - YouTube

Could this be a bent axle? Or is it pretty much the crank that is toast?