Plug cap device for internal combustion engine

摘要

There is disclosed a plug cap device (11) for an internal combustion engine wherein a bore (15) receiving a corrugation portion and a cylindrical portion of an insulator of a spark plug has a first portion (15a) corresponding to the corrugation portion and a second portion (15b) corresponding to the cylindrical portion such that the inner diameter ( phi P) of the first portion (15a) corresponding to the corrugation portion of the insulator is slightly smaller than the outer diameter of a major diameter portion of the corrugation portion and such that the inner diameter ( phi Q) of the second portion (15b) corresponding to the cylindrical portion of the insulator gradually decreases from the inner diameter ( phi P) of the first portion (15a) toward an insertion opening at which the spark plug is inserted to provide a tapered configuration, whereby the plug cap device (11) insures an improved electrical sealing property and provides high operating efficiency when fitted over and removed from the spark plug.