do i have to replace the crank pully bolt if i change the crank pully or can i reuse it?

 

you can reuse it no problem..its not a tampon or a condom

 

nope, it's reusable. You'll know if a bolt needs replacing when you look at the torque specs. If it states a torque rating plus a degree number, then it's probably a torque-to-yield bolt. That means that the bolt is torqued down a bit more, stretching it and providing maximum clamping force.