Spark plug boot with ventable seal

An ignitor assembly positionable in a spark plug mounting bore formed in a cylinder head of an internal combustion engine for connection to a spark plug, comprising:

• an ignitor body including a first end portion and a second end portion;
• an ignitor coil mounted on said first end portion of said ignitor body;
• a sealing boot mounted on said second end portion of said ignitor body including a boot body having an outer surface positionable adjacent an inner surface of the mounting bore when said sealing boot is positioned in the mounting bore, said sealing boot further including at least one annular sealing rib extending radially outwardly from said outer surface of said boot body for engaging the inner surface of the mounting bore to form a seal joint, said annular sealing rib formed of a flexible, resilient material and including a sealing and venting means for preventing passage of contaminants through the seal joint in a first direction axially along the mounting bore while permitting venting of gas through the joint in a second direction opposite said first direction, said sealing and venting means including a radial length and a width of said annular sealing rib, said radial length and said width being of a predetermined size for causing said sealing rib to deflect toward said second direction when installed in the mounting bore, for causing said sealing rib to be biased into sealed abutment with the inner surface by pressure forces of contaminants acting on one side of said sealing rib and for causing said sealing rib to be moved away from said inner surface when gas pressure at a predetermined magnitude acts on an opposite side of said sealing rib.