oily bores

["Slack Alice" Simon]

This type of ring (tapered) is called a wiper ring, I think.

I understand that it’s job is to seal and wipe the bore clean of excess oil.  If fitted upside down it wipes oil up into the combustion chamber rather than down into the sump with obvious results.

I think the chamfer decreases the area of the ring in contact with the cylinder, so increasing the pressure on the cylinder wall, so making it a more effective "wiper".

Simon