Crank case pressure

[yao]

Hi all,

While changing oil this weekend, I notice that I have tremendous amount of Crank case pressure via Oil fill plug.  Can anyone verify this is normal?  Just start your scooter with oil fill plug open and tell me if there is any pressure coming out of it.  Thanks.

[CROSSBOLT]

Yow, Yao! That's the air volume displaced by the piston on the down stroke. It sucks in when it goes up but not as noticeable since there is no oil spray to watch. Hard to ignore but spectacular, hey?

Karl

[LidoCA]

 I once the started the engine with the oil fill plug off. I spent the next hour cleaning oil off of everything within 6 feet of the scooter.

[yao]

So it's normal then.... weird, My Buell didn't do this and none of my cars does.  Usually if there is that high the crank pressure, means there is a lot of blow by in the piston.  But, it rides fine, no oil burning, gas mileage didn't drop and power is the same.  That's why I wanted to verify with people on here..

[ole two wheels]

Hi Yao. There are at least two things you DON'T do while a bikes motor is running. #1 Touch the tip of the spark plug and #2 Remove the oil filler plug. Thank you LidoCa.   As Crossbolt said, crankcase pressure is a result of the piston movement. You have a line, hose, or pipe running from your valve cover back to your intake. When the piston is in the intake stroke of the 4 stroke cycle it sucks the pressure from the crankcase in with the fuel/air mixture and is detonated for the power stroke and expelled with the exhaust gases. In the fifties and prior, that pressure was vented to atmosphere, then the EPA  started helping us manage our lives and all that started changing and continues to this day.

Mac, aka "ole two wheels"