Pistons and piston castings

A monolithic piston casting of aluminium or aluminium alloy for forming a piston for an internal combustion engine or compressor and comprising:

• a cast generally cylindrical crown having a ring belt extending around the crown for the formation therein of one or more piston ring grooves,
• two cast gudgeon pin bosses defining a gudgeon pin bore extending through the piston casting in a direction normal to the piston axis,
• two opposed cast skirt thrust surfaces connected to and depending from the ring belt and symmetrically disposed about a plane including the piston axis and normal to the gudgeon pin bore axis,
• each skirt thrust surface extending only part the way around the piston casting and terminating in respective spaced generally axially extending edges,
• cast skirt side panels extending between adjacent edges of the skirt surfaces, the side panels lying in respective planes parallel to, but spaced on either side of, the piston axis, each said gudgeon pin boss extending inwardly of an associated skirt side panel, and
• a projection extending circumferentially from each edge of each skirt thrust surface beyond the associated edge at the end of the edge remote from the crown, each projection being spaced inwardly from an imaginary cylindrical extension of the skirt thrust surfaces to provide a platform for steadying the piston casting while it is being machined.