crankscase breather, whatzitdo?

Dumb question here. The obvious answer is that it lets the crankcase breath, but what exactly does the crankcase breather do? How much oil is supposed to go through it? Is it there in case oil gets past your rings? I have a little black oil and dirt mixture around the top of my tranny where the breather hooks up, I assume this is just from a poor connection or plugged hose which I will look at tonight, but is there actually supposed to be oil going through it?

I have noticed that when I fill up my oil in the bike, the next time I ride the oil comes out somewhere right around the breather. I end up with still enough oil, but it is at the bottom of the sightglass, not in the middle anymore, at which point the leak stops. I am not sure if it is coming out of the breather, but cant see anything else around it that could be letting it out. The bike runs fine, it is not rnning out of oil, it just always spits out the excess...

When you add oil is the bike one the centerstand on level ground? Ed

no, my centrestand is gone (PO) but when I check the level I pull on the handlebars till the bike is level. You think maybe I am adding too much oil? I added 3.7 litres on my last oil change (new filter).

Truth be told, it is acting like I am ading too much and is getting rid of the excess, but I don't think I have too much in there.

The symptoms sound like too much oil, but I guess it could be some other problem. Maybe some others on this site have ideas. Ed

Thx. Like I said, the bike is level as far as side-to-side goes, but it may not be perfectly level front to back. I park her in neutral and she doesn't want to roll, so I thought that was level enough.

Assuming I am just adding too much oil and the bike is getting rid of it through the breather, is this what it was designed to do? is it normal for oil to actually go through there, or is it just supposed to be hot air venting out?

As you mentioned it allows your engine to BREATH. Engines will have a minamal amount of Blowby,thus causing oil vapors to exscape out the breather. By being connected to air filter housing it helps to eliminate pollution of oil vapors by directing those vapors back into the engine to burn. If you have any slight leak around breather tube,oil residue will collect as will dust and road grime causeing unsightly visual unbeautiness.( Messy oil covered area ). Moisture is also released through the breather sometimes forming a foam like gunk.But by the releaseing of that moisture it helps the oil not to be as corrosive, as water in oil will cause a corrosive acid inside the engine if not properly vented to allow moisture to escape.:blink: .:blink: