I’ve posted a while back about my engine bogging after a rebuild. I eventually found that I had oil pooled up on top of 3 of 4 pistons causing it to fluctuate in rpms before dying out. I done leak down test and roughly pointed it to be the piston rings. By now I’ve pulled the head off again and there is no oil in the cylinders. Cylinder walls don’t look damaged. Although it has a slight glazed looking rings around all cylinders I assume froM it being bored over. What would cause oil to pool on the cylinder like that? Bad rings or valve stem seals? Or will oil get into the cylinder while the rings are still seating themselves?

EDIT: remanufactured head sent ready to install. 2001 2.5l Ranger.

 

Oil couldn't "pool" on pistons if it was rings, only valve stem seals fit that description

Oil is sprayed on to the cylinder walls by the connecting rods and pins, but under the piston, the rings scrap off the oil, on the way down, if rings are failing then some oil can remain on the cylinder walls and is burned with air/fuel mix, can't see it "pooling"

Valve guide seals prevent the negative pressure in the intake manifold(18" vacuum at idle) from sucking oil, in the valve train area. down the intake valve stems where it is pulled into the cylinders on intake stroke
When engine is off this oil could drip down onto piston top if intake valve was open

 

That’s what I was thinking but obviously wasn’t too sure. Do you think I should just change the valve stem seals or get the rings while I’m practically there?

 

You have to pull the engine to do the rings, so you are not "practically there"

What were the compression test numbers, or the leak down %