My engine started blowing oil out the breather at about 40 hours. The upper rings and ring lands on all pistons had worn significantly allowing “Ring Flutter” at reduced manifold pressure on descents. This would only occur in flight, so it was difficult to diagnose until a manometer was tapped into the crankcase vent line about 2’ from the outlet. Crankcase vent pressure was stable until manifold pressure was reduced, then it spiked as ring/piston blow-by occurred. The fix was replacing the Performance Engines supplied forged aluminum pistons with stock design ECI steel/aluminum pistons. I now use about 1 quart of Phillips XC in 15 hours.
Steve Colwell Legacy 550
On Behalf Of Charles Brown
Re: L2K oil under belly