bad leak down numbers and oil usage

Rotax Wizard wrote:

Walt, perhaps you have me confused with Sean?

Oil pressure is not what causes crankcase pressure.  It is crankcase pressure that drives the oil return to the oil tank.  The area of the cylinder head does not have any oil pressure.  Once the oil lubricates the rocker arm it is dropped out and loses its pressure for the return via the push rod outer tube into the crankcase.  if the engines internal pressure, created by piston blowdown of pressure past the rings, exceeds the limits then oil can be forced past the umbrella seal into the back side of the valve.  The "leaking" is then caused by this higher pressure.  

Cheers

I ran the crankcase pressure test today, I was not able to achieve 266f oil temperature. On the ramp at 188f oil temp the pressure was 6.3 lbs.

UPDATE;

My plan was to remove the cylinder heads and at a minimum lap the valves. While that far with the disassembly I would pull #1 piston and see if there was anything obvious causing the low leak down numbers. Upon removing the piston I discovered the middle and oil ring were both stuck on the lower side. I removed the piston from the rod and on closer examination I found the spacer between the top and middle ring broken and just sitting in place. This piece was riding there but fortunately couldn’t escape to cause further damage. Upon this discovery I removed all pistons for inspection. Cylinder #3 was slightly sticking on the middle ring. The rings on cylinders #2 & #4 were fine. 

This fracture in piston #1 is very rare maybe a metal issue. Since all the piston were from the same lot I felt it safer to replace all pistons. The rings  come with new pistons so they were replaced also. The cylinders were all in good shape and all the guides and bearings were very tight. The final work was walnut shell blasting the heads to new condition, ultrasonic cleaning the valves and lapping them. All new gaskets and valve stem seals. 

In all I spent a little under $2k. My total down time was 7 days. Brett at Advanced Powerplant Solutions was extremely fast getting the parts to me. I did all the work with the engine still on the plane in my hangar. My ace in the hole was Bryan Toepfer, half way around the world who I bugged endlessly with questions through messenger. 

The first run and flight was yesterday for 1.0 and everything is good. I’ll put a bit of time on it and follow oil consumption and leak down to confirm if there are any issues. 

Good effort. I'm glad you got it fixed. If there is no damage to the cylinder then you should get another 1600 hours.