don46 is correct, can't be done. The porting in the crank would never line up.. The crank is smaller, the gears are crap compared to your 500.. Check ebay out for a lower crank. Your issue could be small, invest in a crank split tool and get to work. That's all I can say with what little info we have.. Post up some more info about your problem and maybe we can help get to the bottom of this.