Aluminum bore engine having wear and scuff-resistant aluminum piston

A reciprocating engine having a first aluminum alloy block, at least one internal cylinder wall in said block comprising said first aluminum alloy and defining a cylinder bore, and a second aluminum alloy piston reciprocating in said bore, said wall having an arithmetic mean average surface roughness, R.sub.a of 0.09 to 0.25 micron, and said piston comprising a skirt having an external surface confronting said wall, said surface having a first hard anodized coating adhering to said surface, and a second composite polymer coating atop said hard anodized coating and comprising a plurality of solid lubricious particles in a heat resistant polymer matrix capable of withstanding the operating temperatures of said engine.