There has been some confusion in the trade concerning piston ring seating. Hastings Manufacturing has had ring sets sent back with the comment "the rings didn't seat,"however, when the rings are examined they have 360 degree continuous contact on the O.D. face. This contact is indicative of total ring sealing.
So when is a ring, so to speak, seated?
For a compression ring to seal against the cylinder wall it is important that line contact be established. The sketches below Illustrate cross sections of two popular types used in many ring sets.
As can be seen, both the barrel face and the taper face will initially only make line contact with the cylinder wall. The contact area will increase as ring wear occurs, however. It will under normal operating conditions be many thousands of miles before the ring is worn to full O.D. face contact. In fact when a ring is worn to full face contact it is near the end of its service life or has experienced some form of abrasive wear.
When proper cylinder finish is achieved during the honing process the rings will line contact in a very short period of engine operation.