Ceramic capped piston

Claim 1

A piston assembly comprising: (a) a ceramic piston cap including: a cylindrical cap section having upper and lower surfaces, a downward facing extension attached to the lower surface of the cap section, and an outwardly extending first radial flange attached to the extension and spaced from the lower surface of the cap section, said flange including a first contact surface which faces toward the cap section; (b) a metallic body including: a cylindrical body section having an upper surface with a central opening therein defined by a wall portion and a lower platform, a second radial flange extending inwardly into said central opening from the wall portion, said second flange extending into the space between the first flange and the lower surface of the cap section and including a second contact surface which faces away from the cap section; and (c) bias means for forcing the first contact surface against the second contact surface; wherein the first and second flanges are configured so that contact between said flanges is limited to said first and second contact surfaces, whereby the assembly can accommodate differential thermal expansion of the piston cap and body while maintaining continuous contact therebetween; wherein said bias means is a spring located between said lower platform and said downward facing cap extension, wherein said spring forces said cap away from said body.