Hi All, Two weeks ago the nut on the clutch boss came loose on my sons 05 YZ250F and tore the splines off the Hinson boss. I replaced it with a standard Yamaha boss and since the rebuild it won't go into 5th gear. You can select all gears with the engine not running but when the bike is moving it will not move to 5th. Occasionally it will grind as though its half into gear (if that makes sense) but doe's not drive the bike. Is this a gearbox problem or could it be something i did with the clutch ? Regards. Mike.