all my old british stuff runs open breathers, no filters, just a tube sufficiently long to exceed the tidal volume below the pistons. most breathe through a tube from the primary chaincase, which receives pulses through an open drive side main bearing.
on my race motors i drill the crankcase and rocker boxes for breather lines, and run them to a catch bottle behind the motor somewhere.
some people put a one-way valve in the breather hose, but it isnt there to ensure a one-way circulation, because there is no unvalved entrance to the crankcase. rather the idea is to pull a partial vacuum in the crankcase to reduce oil leakage.
on my race motors i drill the crankcase and rocker boxes for breather lines, and run them to a catch bottle behind the motor somewhere.
some people put a one-way valve in the breather hose, but it isnt there to ensure a one-way circulation, because there is no unvalved entrance to the crankcase. rather the idea is to pull a partial vacuum in the crankcase to reduce oil leakage.
