Breathe in Breathe out

Not a mysterious eastern technique involving staring at a blank wall and emptying your mind, no instead I have been staring at the inside of the Sizaire crankcase trying to fill my mind with the ancient French methods of crankcase breathing.

Single and twin cylinder engines have problems with the huge pressure spikes in the crankcase causing loss of power and oil leaks and probably other things that I have no idea about. Generally old engines have lots of vents to handle these spikes and oil leaks were just a way of keeping the dust down.

The Siz has two vents with one way leather flapper valves attached, one allows air out but not in and the other works in the other direction sucking in air and more importantly oil out a reservoir that catches the leaks from the rear main so it works like a scavenging pump, this one has never worked.

So on my car, instead of the oil being sucked back inside the engine it is sprayed over the entire underside so no drip tray is big enough for this car.

In the last picture you can see Colin has recessed the area where the valve is going as there was not enough clearance due to mods done by others.

The question is if I use leather, what type or is there a synthetic that would work better?


Suction Flapper Inside Crankcase



Location of out going flapper, recessed due to clearance problems with flywheel


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