HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
gmoney911

2006 YZ450F Oil Coming Out Of Breather Tube

2 posts in this topic

I just went on a 3 hour ride and when I got back home I noticed there was some oil coming out of the breather tube. I was wondering if this is normal and what causes it? Or do I have a problem on my hands? Thank you.

Share this post


Link to post
Share on other sites

It is normal. The piston displaces 450cc of air under it as it goes down, just like the air it displaces over it when it goes up. You can look at it as if it had an intake and exhaust stroke underneath the piston as well as above it. It is the function of the breather tube to allow that air to move in and out, at least part of it, so as to reduce the pressure in the crankcase. The other reason it's there is that the rings leak, no matter how good they are. They don't leak much but they do, and the combustion gases that get into the crankcase have to be allowed out.

So, at high speed, there's a lot of oil flying around in the cam box, and some of it gets caught in the air flowing out the tube during a pressure pulse, and if it gets far enough downstream before the pressure reverses to a vacuum, it will stay in the tube. Eventually, this builds up to the point that there's enough to drip on the floor, and there you have it.

Other things that are normal include your header glowing red (visible in twilight), or the radiator overflowing, either one after more than 90 seconds of idling.

BTW, welcome. Read the rules, read the Common Threads Sticky, learn to search, and enjoy using the forum. :thumbsup:

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0