Here, you can see a different example of wearing damage to a piston ring seal groove – in this case, the face on the inside of the groove has been worn away, so that it now has a lipped edge.
As in example (a), this kind of damage has a number of different causes, from general wear and tear, and excessive play/wearing in the journal and thrust bearings, to contaminated or carbonised oil getting into the piston ring seal area.
Over time, this wearing will become gradually worse, affecting both the efficiency and output of the turbocharger. Generally, it isn’t economically viable to repair wearing damage like this, and it’s much more cost effective to replace the affected piston ring seal.
In addition, it’s also important to identify the cause of the damage, so that it doesn’t happen again, which may mean making repairs or replacing the thrust and journal bearings.