I did the same thing a couple weeks ago on my 490! I don't know if you have to take the cluch off on your bike, on mine you do though.First,drain you trans oil, take of the side cover, then the clutch plates and basket, unhook the spring on the shaft and pull it out. It is simple if you read the manual and take your time. I got a new shaft from my yamaha dealer, it was 70 bucks :| When you go to start your bike, find compression and then PUSH the starter down quickly. don't jump on it! you can leave the motor in the bike, you will need a big socket for the clutch basket if you have to take it off. for loosening the clutch basket, put it in top gear and have someone hold the back brake on for you. while you are waiting for the part, just roll your bike down a hill, put in second gear, and pop the clutch, it will start right up, just don't kill it on flat ground...Good luck on getting it fixed, yamahonky