bad,
changing the oil, DEFINITELY. The one "achilles heel" in these bikes is that the crankshaft and the cams ride directly on the crankcase and head material, which is aluminum. There are no replaceable journals like some engines, just the cam and crank against aluminum. Therefore, if you neglect your oil, and screw up your head or crank, you can't just go out and replace the journals, you have to replace the whole head. SO, it comes down to that money for oil buying you peace of mind or not. As for the valves, well, if there is too much slop or too little, you can damage your valves, or your pistons among other things.
