Fabricating internal combustion engine cylinder heads with close tolerance internal surfaces

A cylinder head for an internal combustion engine, comprising:

• (a) A head structure having at least one gas passage provided with a recess for a valve seat insert and a guide bore for a guide sleeve insert;
• (b) sintered powder metal inserts implanted respectively into said valve seat recess and into said guide bore, the internal cylindrical surfaces of said inserts being true with respect to each other within a locational tolerance of 0.001-0.002 inches, and finished to a surface accuracy within a tolerance of 0.002-0.003 inches, the internal cylindrical surfaces of said inserts having open porosity that constitutes 5-22% at said surface area;
• and
• (c) means to introduce lubricant to the internal cylindrical surfaces of said inserts whereby the porosity in said surfaces may act as reservoirs for a constant lubricant supply.