Cylinder block with unlined piston bores

A cylinder block for an aircraft engine with unlined piston bores comprising:

• an aircraft engine cylinder block comprised of a steel material and having a main body extending along a longitudinal axis with a first end and a second end facing opposite from said first end, and wherein said main body includes a splined bore to receive a rotating shaft wherein said splined bore is formed generally at a center of said main body to define said longitudinal axis, and including a plurality of piston bores formed within said main body in an annular pattern about said longitudinal axis with each piston bore defining a bore axis that is parallel to said longitudinal axis and wherein each of said piston bores includes an open end facing said second end and an enclosed end facing said first end, and wherein each of said piston bores is machined to a rough shape with said aircraft engine cylinder block including a heat treated surface to provide a desired bore surface hardness, and wherein each of said plurality of piston bores is finish machined to a predetermined surface finish to define a final bore surface, with said final bore surface and said main body being formed from a unitary piece of material;
• a valve plate attached to said second end and positioned to be associated with said open ends of each of said piston bores, and including a diffusion bond formed between said second end and said valve plate;
• and
• a plurality of pistons comprising one piston mounted within each one of said piston bores, and wherein each of said pistons includes a steel piston surface that is in direct sliding contact with said final bore surface.