Combustion chamber distance control for combustion-powered fastener-driving tool

A combustion-powered fastener-driving tool, comprising:

• a combustion-powered power source including a cylinder head and a combustion chamber defined by said cylinder head, a valve sleeve, a cylinder and an upper surface of a reciprocating piston;
• said valve sleeve reciprocable relative to said cylinder head between a rest position and a pre-firing position;
• said valve sleeve having a range of positions between a first sealing position in which said combustion chamber is closed, and said pre-firing position in which said valve sleeve is prevented from further movement;
• a lockout device associated with said power source and having an actuated position configured for preventing the reciprocation of said valve sleeve beyond said first sealed position to open said combustion chamber, but permitting movement of said valve sleeve from said first sealed position to said pre-firing position until said piston returns to a piston pre-firing position post combustion;
• and
• said lockout device is located in operational proximity to said valve sleeve and includes a retractable latch that engages a shoulder of the valve sleeve upon actuation, said lockout device being located a proscribed distance below a disposition of said shoulder in said pre-firing position for permitting upon actuation said movement of the valve sleeve from said first sealing position to said pre-firing position.