Kibblewhite has researched, tested and chemically separated several cast iron blends, and ultimately specified a combination of ingredients to meet the needs of Harley-Davidson engines. KPM material includes specific amounts of key elements such as carbon, silicon, manganese, nickel, copper and sulfur to create a highly pearlitic structure wit dense fine grains for excellent wear resistance. This "recipe" also allows for a superior surface fnish in the guide bore that is easy on valve stems.

These Knucklehead style cylinder heads are precise reproductions of the stock counterparts and show all the small details like cast-in number tags and foundry markings. Thus they make for great replacements for your worn top end or to build a factory look-alike engine. They are manufactured after 1940-1947 heads with large intake ports. The pre-installed, but unmachined valve seats are sized for stock intake and exhaust valves and hardened for the use of today’s unleaded fuels.