died yesterday cruising at 45. nothing siezed and no sounds or warnings. just dies. so installed new plug. when starting would die again right away, even with new plug. then pedal crank let go. felt like something inside broke (but what? its one piece yea?). now crank so loose cant start and chain wont stay on, but can chain coming off keep bike from running once its on? will new bushings tighten crank position?