Michael,

Tests for cowl air pressure penetrating the case have been inconclusive so
far. The latest attempt to find a crankcase air leak was a very sensitive
test instrument pulling vacuum on the crankcase while I hosed down every
penetration point on the engine top and bottom with a high volume air
compressor.

The balloon and soap suds test found a very small leak where the steel tube
for the rubber vent line enters the dip stick housing.  JB Weld fixed that.
When aluminum tape was applied to the Dipstick to Dipstick Housing, tie
wraps were also used for double security during the flight test. Steve Colwell  Legacy  916 505-6099



You Said:

During runup and takeoff roll the manometer (tapped into the crankcase vent
about the mid-point of its length) will read zero until plane has about 120
knots indicated airspeed.  At 120 to 200 knots the manometer reads 4" to 5"
with a MOMENTARY spike up to 14" to 20" when power is reduced in the
pattern.

This symptom suggests that airspeed is pressurizing the case and pushing oil
out. Check the Oil filler cap for a proper gasket and for proper sealing of
the gasket.