do you have a "sand seal" on the pulley end of the crankshaft?....if not, even with a "real" filter, *I*(personally) would not stretch the oil change intervals toomuch if any at all....the crankcase is still open and ventilated by outside "dirty" air.....
------------------- Chris Perdue "I'm ever so thankful for the Internet; it has allowed me to keep a finger in the pie and to make some small contribution to those younger who will carry the air-cooled legend forward" Jim Mais Feb. 2004