My friends 2004 polars sportsman 700 just started burning oil and making a knocking noise when he was using it to plow. what might be the problem? thanks for your help. I am very mechanically incline so im going to fix it my self . It would be good to know where to start looking tho thanks. My guess is a broken or collapsed piston skirt or broken rings. the engine still runs.so my question was it their a common thing that goes wrong with them. thanks again