I think I have found the problem cause and the solution
and unfortunately, it is NOT as simple as the oil laberynth, or the valve cover. I will try to explain my experience in english (I am a native speaking person, so forgive me if I am not clear enough), and from the point of view of an MD who has been forced to learn mechanics...:-/
My first advice to all of you who have the oil in the filterbox problem in a relatively new 850 XP, is to get an accurate compression reader and measure the comprssion rate in both cilinders, full throttle. If it is anything less than 200, forget about the valve cover; that is not the problem, but the symptom.
There are a number of 850's (unknown) who SEEM to have come with a problem in the cylinders' nicasil layer finish, which roughen's up against the pistons. Cylinders get scratched (I've seen several engines opened, and they looked scary), combustion messes up, piston head's get carbonized, and compression is lost.
Pressure is then passed down along the creaks between the piston-cylinder (like if you had worn-out rings), all the way down to the carter. Carter pressure build-up transmits to the valve chamber, and when it mounts, it collapses the oil laberynth inside it, and starts flowing through the breather hose. Then, it starts spitting air and oil in the air-filter chamber.
So.....if you have oil in the chamber and the cylinder pressure readings are low, forget about ONLY changing the valve cover. Today I have changed the whole cylinder / piston / crankcase (basically the whole engine aside from the rods and the crankshaft). Pressure in the cylinders skyrocketed from a puny 125 before the change, to 230 psi. Idle rpm stopped fluctuating (I used to have from 950 to 1200, the lower end being when the piston cicle receives less presure) and is now clockwork, oscillating between 1.180 and 1.200. Sound is different. Oil spitting has stopped.
IF your compression is right and you still have oil, it might be solved by just changing the valve cover. But I would rule out compression problems first.
I will be doing a 4-days mountain expedition starting this Thursday. My air-box is now clean. Keep your fingers crossed and by Monday I'll let you know how I fare (and I am going to check compression again when I come back).
This seems like a bigger problem than Polaris has aknowledged to date, and at least in my country, nobody knows why. But 9 engines have been shipped in to replace other engines in 2010 models, like mine.
Hope this helps.
Last edited by Dogoman; 03-22-2011 at 05:12 PM.