Abstract: An internal combustion aircraft engine comprising a cylinder head having a cylindrical head bore formed therein, a piston, and spark plugs, the cylinder head bore and piston designed to reduce engine knock. The cylinder head is fixedly attached to a top end of a cylinder barrel formed with cylindrical walls, the cylinder head bore and the cylindrical walls defining a cylinder. The cylinder head bore has formed therein an outwardly protruding cavity with respect to the top end of the cylinder barrel. The piston has a piston crown, and the piston contained within the cylinder, the piston crown, the cylinder walls, and the cylinder head bore define a combustion chamber. The piston crown has a concavity formed therein, and the piston is constructed and arranged to reciprocate within the cylinder. The concavity of the piston crown and the cavity cooperate at a top dead center position of the piston to form a swirl chamber.

Abstract: The present invention relates to an improved method for the manufacture of aircraft engine cylinder barrels to prevent their premature failure due to hairline cracks or specks thought to be caused by caustic stress corrosion cracking during black oxide treatment. Machined aircraft cylinder barrels immersed into a black oxide chemical bath composed of a solution containing about 60% sodium hydroxide, about 0% sodium nitrate, and about 40% sodium nitrite most effectively prevents specks and hairline cracks. Since residual stresses from machining also contribute to the probability that specks or hairline cracks will occur during black oxide treatment, the maximum selected number of cylinder barrels essentially free of detectible specks or hairline cracks determines the maximum number of cylinder barrels to be machined on a given set of tool bits.