'08 450 with oil in the airbox...

So...  I just got finished with a top end on this bike (cylinder re-nic'd, new piston/rings, etc...) and have been riding the ice up here in Alaska.  My bike has been un-corked and runs like a champ. The one problem I'm having though is consistent oil in the airbox, enough to leak out of the bottom of the access door.  I know it's coming from the breather tubes, but I'm not 100% sure why I'm getting it.  Riding the ice, the bike spends a lot of time at high RPM and lays over (dragging pegs occasionally) in the long sweeping corners. My most recent thought is that I screwed up the rings when I put the top end back together and I'm getting combustion gas pressurizing the case.  When I put my finger over the breather at idle I can feel both positive and negative pressure on the breather though.  My hope is that I have not been checking my oil level correctly and I just have a little excessive oil.  I'm working on borrowing a leak down tester so we can check the rings, but I'm not sure what else it could be. 


Any thoughts?

Probably as you said: you are not draining the oil completely, and are possibly over filling, and you are in high rpms, etc.


Do what the YZ does and re-run the vent down by the skid plate, or up under the tank higher than the motor.

I have always had this issue.high revs and long wheelies are my reason for it.i did a search on websites and found a overwhelming number of people with the same scenario ,who were using their bike in the same way and had same prob.AS mentioned above,run hose down frame.its not good over oiling your air filter lol

I maintain twelve of these bikes, and occasionally a coworker steps in for me, invariably the bikes display this symptom. The bikes are overfilled on the oil level. Use the manual change the oil and filter, and if you add more than one quart, it's now overfilled.

Yes, it says 1.2 in the manual with filter change, but it is .2 too much IMHO

Yup yup yup. Overfilled put away the testers.

Thanks guys, my last change was just drain and fill, no filter change. According to the manual it is supposed to take right at 1 quart. I put about 28 oz in and it was at the top of the hash marks on the dipstick. I guess I'll start with 1/2 qt next time. I'm guessing I have had about a cup of oil exit through the air box at this point.

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