A friend of mine. Has a 2006 crf450. He changed the oil. Then went out riding and oil started coming out of the air box. He thought he might have put the oil filter in backwards. He checked it and he found that there was metal in with the oil and filter. He rebuilt his engine top and bottom end about 30 hours ago. It just seems strange this happened after an oil change that it started doing this. Anyone have any ideas.