Here's another item you might want to replace when you are changing out your front sprocket. Because of it's big back tire, the chain is further away from the center of the engine than most bikes. The engineers at Yamaha decided they had better support the end of the countershaft since it is cantilevered out there so far. They also figured they had better feed some oil out there as well. These Countershaft Seals keep that oil where it belongs, lubricating the countershaft outer support.