I made a post in another section but I was told to post here so I'll try. I have a 20" Bmx. Just bought a new back wheel for $400, Now I've run into another problem. The crank arms have become really loose and wobbly, so I decided to try tighten them but when they are tightened they jam up at the apex point of pedaling, and It will stop my flow of pedaling and I will have to use a lot more pressure than I was using to pedal. Any Idea what this is and What I have to do to fix it?