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Hey all - new to the forum here. A lil about me I've been riding, racing and repairing Atv's, Jet-ski's, and snowmobiles most of my life. Just another adrenaline junky who loves to have fun.

I have a specific question that I need some help with. I have an 2004.5 Sportsman 500 HO. After my last ride I found about about a half quart of oil in my air box. After inspecting the vent lines, the one from the oil reservoir was a little restricted as it had gotten pinched between the gas tank and frame so I re-routed it. Unfortunately this did not remedy the situation. I believe the breather line to be free of restrictions. So my question is what would cause my crankcase to build pressure and push my oil out into my airbox? A blown head gasket? Any info would be greatly appreciated.
 

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I have the same problem on a 1998 500. I haven't had time to look at it yet. I am going to do a compression test and take the rocker arm cover off and look at the cam lobes, if not that I am going to look at possible head gasket leak. I bought this atv not running so another possibility is a stuck ring. The only thing else I think is it may have flooded out and washed the rings down with gas. Sorry I couldn't help you more. Thanks
 

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I would asume it's blow by from crank case pressure. You could have bad rings, valve guids, valve seals. Or maybe excessive pressure from over filling the oil. If a vent is pluged it will pump oil. I dont know much about the polaris but these are a few tcauses
 
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