Crank Case overflow full???

[kineo3]

I went for a 50 mile ride this weekend on my 400EX. To make a long story short, I noticed oil coming up through my crankcase overflow into my airbox, and draining into my airbox drainplug. It filled my drainplug about 3 times. I had this problem before, but I thought It was just to full of oil. I got the machine used and have not had a lot of time to ride but I thought the problem had gone away after I drained a little oil out. I was wrong! I plan on changing the oil and keeping the old stuff to measure how much was in the machine. My question is ... Is there anything that could be broke, plugged, warped, twisted, bent, that could be causing the oil to be forced up through the overflow. It is as if there is to much pressure for some reason. Please Help.

[400exdad]

You're on the right track regarding the amount of oil that is in the motor. A 400, being a dry sump is tough to check the oil in. I can tell you this, that if you drain the tank and gear box, and replace the filter, it will hold exactly 2 quarts. As a matter of fact, I had to start mine to get the last bit in.

To check the oil, run the motor at idle (no revving) for 5 mins or so, shut it down and check the oil. That is by the book. If you rev it there will be too much oil in the case and the tank will appear low.... There is another check as well.. from memory... If you'll look below the filter on the motor, you'll see a 8 or 10mm bolt with a gasket on it. This will check the oil in the case after it has been idling awhile (5 min.?). The oil should be just at this check hole. If it's not, it is either too full or something is wrong. I think there is a check valve or 2 that could go bad. Good Luck :)

[kineo3]

Thanks for the response, all info is welcome.

[oynot400]

I just went through this on my Rancher. It was pumping all the oil out of the crank case into the air box. What caused this was combustion gas, blow-by, was pressurizing the crank case and pushing the oil out the breather. One of two things are causing this:
1. exhaust valve or seal is bad or
2. rings or cylinder is out of round.
It was a combination of the 2 for my Rancher. The vavle seat fell out and the seals being bad. Then the cylinder was wore out of round.
Hope this helps......:)