Keith Black Dome Top Piston Kit For Harley Xl1000 1972-1985 Keith Black dome piston set is standard size with a 8.2 compression ratio. The 390 hypereutectic alloy is cast in a permanent steel mold which makes it possible to build a light weight piston that makes more power and uses less fuel and lasts longer. Pistons are standard size, for a 3.188 bore and has a 9:1 compression ratio. The low heat transfer of the alloy keeps the skirts cool so piston expansion is minimal. The combination of a low heat transfer piston alloy and high compression ring placement increases power and economy. The high ring placement alone reduces detonation and increases the top ring temperature. Features: Manufactured from high-strength, T-5, heat-treated, 390 hypereutectic aluminum alloy Allow a tighter fit and longer piston and ring life Diamond-machined pistons are held to plus or minus one gram weight and less than one-half-thousandth inch (.0005) tolerances from piston to piston Each kit contains two pistons, pins, spiral-lock pin clips and Hastings moly rings Replacement piston rings and pin lock rings available separately Note: KB pistons can be installed tighter than other pistons. This results in less piston rock and better ring seal. Please read instructions included with piston for correct piston clearance. Note: Due to the thermal conductivity and design of KB pistons, special attention is required to the top ring end gap. Please read instructions furnished with piston for correct ring installation. Note: Run engine at moderate speeds for at least 500 miles, avoiding excessive running in lower gears, in order to properly break-in new pistons and rings.