The crankcase volume of an eight cylinder engine> is constantly changing, so it 'puffs' at the breather. A six cylinder> engine maintains a constant volume and doesn't puff so much.

John Ings wrote:>

Uhhh..... I don't think so.>

Any engine that is a) even-firing, and b) has an even number of > cylinders greater than 2 always has a piston moving up at exactly the > same rate as every piston that is moving down throughout the cycle, so > the crankcase volume is constant.

I *think* it may even be true that the net crankcase volume for an odd > number of cylinders greater than 1 is constant, but I'm not positive > about that.

Steve <no@spam.thanks> wrote in news:mrqdnVTAdcRSDu­rfRVn-vw@texas.net:>­

It may be more correct to say that the volume is constantly *displacing*. > Churn may result in at least some of the puffing.

An exception: Those Harley twins where both pistons can be moving in the > same direction at the same time.

TeGGeR® wrote:>

agreed, although that's pretty well damped out between the bottom of> the crankcase where the "churn" is and the top of a valve cover where> the breather usually is.>

If there's a distinct "puffing", I would suspect a cylinder with> higher blow-by than the others.>

Not an exception: note that I said "even number of cylinders greater > than 2" specifically because 2-cylinder engines have pistons moving > together instead of opposite to each other. And I was thinking > even-firing ones like old John Deere 'Johnny Poppers' and other bike> and small air-cooled engines- those odd-firing Harleys are a case unto> themselves!>

TeGGeR® wrote:>

agreed, although that's pretty well damped out between the bottom of> the crankcase where the "churn" is and the top of a valve cover where> the breather usually is.

If there's a distinct "puffing", I would suspect a cylinder with> higher blow-by than the others.>

Not an exception: