Sorry, I was staring @ that Norton so long I didnt realize you had posted words too! Thats a great bike. The grinding on the 550 could be something with the clutch? Which isnt too bad to deal with, but I ouwld think it would do it in every gear if it was that? Or it might need the 4th gear/trans redone. Hard to say with out hearing/seeing it. If the price is good though I would pick it up. If it ends up being something more than you want to deal with you could make $$ on parting it out. As far as common goes, I dont know? Old Hondas are tanks! The only thing common is they run forever!