Seemed to fit better as an advanced question. What is the likely hood that the compression rings on a cylinder are in great shape while the oil rings are worn? Would the motor still put out great compression yet allow oil to slide by with the worn oil ring? How common does that happen on these motors? Also would this cause any oil to end up on the thread of the spark plugs? Just some questions for a buddy who is having a problem with oil consumption, yet has great compression and brand new valve seals. Its burning 2 quarts every 3,000 miles and we are trying to decide whether its worn valve guides or a bad oil ring although the compression rings may be fine.

Josh

 

It's possible, when my old motor was put together they gapped the oil rings too wide. I had great compression numbers, but it would burn 2 qts every 1000 miles.

Have you checked the PCV system? These cars are notorious for consuming oil through the PCV systems. Also, FWIW, 2 qts in 3000 miles is within factory spec.

 

A lot of our customers reuse oil rings on rebuilds with no problem. They are after all "bathed" in oil. The difference in endgap opening on oil ring wipers versus top and 2nd rings seen when an engine is torn down is much less. Also, every gap I've seen on oil rings in all normal "high performance" ring sets is huge compared to the top or 2nd ring with no detriment at all judging by the number of engines out there running perfectly fine.

It's the 2nd ring (the scraper) that wears out. It's the "dam" so to speak against oil. So yes, compression could be fine, but it will allow oiling. There is also an issue with some types of compression rings that seal "so well" that oil will migrate into the combustion chamber if steps aren't taken to reduce crankcase pressure by vacuum pumps etc.