My friend has a raptor 250 that he rides regulary with me. Now, he bought it used with no air filter. He rides with no air filter, or use to. (I bought him one last week, forced him to use it). He always rode without one and never even thought about oil changes or valves. Now, I think we are waaay overdueing it with all the maintenance. I hear about bikes blowing up because they ran it ONCE with no air filter. His Raptor still runs like a champ. Is he really lucky or are we being too bike-conscience with all the maintencance we do, and these bikes/quads are really durable?