bad leak down numbers and oil usage

Walt wrote:

This is the back side of the intake valve for cylinder #3, the others look similar. To me this indicates the valve seal is leaking. My plan is to lap all the valves without removing the heads (least invasive), and replace the valve seals. 

Walt, I am confused.  There is no approved method to lap a valve with the head and valve still mounted.  The lapping needs an abrasive grit to remove carbon or other deposits on the valve and valve seat face.  Simply turning the valve repeatedly would perhaps do something but it also will lead to whatever does come off entering the engine in my view.  Unless you can confirm you do not have excessive crankcase pressure then I don't see the value of just replacing seals on the intakes.  They can be defeated if the pressures are too high.  

I still believe your issue may be oil control rings for excessive oil burn.  Generally oil seals are still near new at even TBO.   The only exception to this is if the engine has had an overheat event where the seal can then become hard and perhaps even crack.  It is however your experiment. 

Cheers

Rotax Wizard wrote:

Walt, I am confused.  There is no approved method to lap a valve with the head and valve still mounted.  The lapping needs an abrasive grit to remove carbon or other deposits on the valve and valve seat face.  Simply turning the valve repeatedly would perhaps do something but it also will lead to whatever does come off entering the engine in my view.  Unless you can confirm you do not have excessive crankcase pressure then I don't see the value of just replacing seals on the intakes.  They can be defeated if the pressures are too high.  

I still believe your issue may be oil control rings for excessive oil burn.  Generally oil seals are still near new at even TBO.   The only exception to this is if the engine has had an overheat event where the seal can then become hard and perhaps even crack.  It is however your experiment. 

Cheers

Sean, your opinion is very valuable, thank you.

The oil pressure is fine, 60-65. The oil on the back of the intake valves can only occur if it is leaking past the valve stem seal, or the guides (which you say is extremely unlikely). 
As for lapping the valves in place it is not that uncommon. There are some videos online describing the process. Mike Bush has a very good one posted about 2 years ago. 

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

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

Wizard,

Sorry for the name confusion, not sure where I got that from.

Your explanation makes sense, I will rig up a test rig for the crankcase pressure test and report back.

I  am very flattered at being confused with the technical Gurus - thank you Walt

That aside; I am not convinced that a crankcase breather blockage is a likly scenario.

To acheive a blockage, the crankcase - oil tank - breather, hoses must be crimped/squeezed OR an internal component has come adrift and is partially blocking one of the hosses.😈