Cylinder bore surface structures for an opposed-piston engine

A liner for a cylinder of an opposed-piston engine, comprising

• a piston-guiding bore surface extending along a longitudinal axis:
• of the cylinder;
• an intake port region and an exhaust port region, each comprising a respective circumferentially-extending portion of the bore surface, the exhaust port region and intake port region being disposed in spaced-apart, coaxial alignment along the longitudinal axis;
• an inner bore surface zone including a longitudinally central portion of the bore surface which extends from the exhaust port region to the intake port region;
• one or more injection ports opening through the bore surface in the inner bore surface zone;
• and
• at least one outer bore surface zone near an end of the cylinder
• wherein the inner bore surface zone has a different surface finish than the outer bore surface zone.

An assembly for an opposed-piston engine, comprising:

• a pair of pistons, each piston comprising a crown portion;
• a skirt portion with a first end where the skirt portion and crown portion and a second end longitudinally separated from the first end, the second end being an:
• open end of the piston;
• at least one compression ring in the crown portion;
• and, at least one oil control ring in the skirt portion near the open end;
• and
• a cylinder, the cylinder comprising a bore surface for guiding the pair of pistons in opposing directions;
• an intake port and an exhaust port, each port comprising a generally circumferential array of port openings through the bore surface, the intake port and exhaust port separated longitudinally along a cylinder axis;
• and, a pair of injection ports opening through the bore surface in an intermediate portion of the cylinder between intake and exhaust ports;
• and
• wherein the bore surface of the cylinder includes at least two zones separated longitudinally along the cylinder axis, each zone comprising a generally circumferential bore surface area contacted solely by a piston compression ring or a piston oil control ring during operation of the engine, and each zone being finished to a different oil retention capacity than the other zone.

A method manufacturing a cylinder for an opposed-piston engine, comprising

• providing a cylinder with a bore;
• designating a first bore surface zone on a bore surface, the first bore surface zone including first and second circumferential port regions concentrically aligned at spaced-apart locations on a longitudinal axis of the cylinder;
• designating respective second bore surface zones near opposite ends of the cylinder,
• designating respective third bore surface zones, each located between a respective port region and a respective second bore surface zone;
• and,
• finishing the bore surface in the designated first bore surface zone to a first surface roughness;
• finishing the bore surface in the designated second bore surface zones to a second surface roughness;
• and,
• finishing the bore surface in the designated third bore surface zones to a third surface roughness;
• wherein, the first surface roughness is greater than the second surface roughness.