We bought a used john deere 612c this season from a dealership in mn. They serviced it and replaced all new cutting blades. After about 50 acres we've had 6 blades broke. The ground we are on has absolutely no rocks. We've talked to john deere dealerships in the area and they have no clue but to replace the bushings. We replaced half of the bushings on one side and they are still hitting each other. Dealership said it had nothing to do with timing. So the only other option that we are thinking is, the mn dealership put blades on for 30" rows instead of 20" rows. Id call the John deere dealership and ask but they are closed.