quote:No. There is not a build-up on the top of the cylinder. About 3/8 of an inch below the top of the cylinder is wore away from the rings contacting the wall of the cylinder. The reason the ware is more at the top of the cylinder is because the ignition of the combustion gas pressure is higher when the piston is at the top. The pressure not only pushes the rings down but it also pushes the rings out against the side of the cylinder wall. The ridge is there because cylinder wall material is worn away, not from build-up.
Originally posted by JavaMan: the oil glazes to the combustion chamber and forms a ridge over time. This ridge will reduce the combustion area in effect raising compression.