Abstract: A tool is provided for loosening or tightening a spark plug while interposing a gasket and a pressure sensor between the spark plug and a cylinder head. The tool consists of concentric, relatively rotatable inner and outer cylinders. The inner cylinder is engageable with the spark plug for rotation together therewith and for loosening or tightening the same. The outer cylinder is lockingly engageable with a cylinder head by means of an axial projection of the outer cylinder and a groove of the cylinder head. The outer cylinder is further lockingly engageable with the gasket by means of a locking leg of the outer cylinder and a peripheral cut of the gasket. The gasket is thus lockingly engageable with the cylinder head by way of the outer cylinder for preventing the pressure sensor from rotating relative to the cylinder head when the spark plug is loosened or tightened.

Abstract: A spark plug with pressure sensor comprising; a center electrode; an insulator placed to enclose the center electrode to support the electrode; a metallic shell having a diameter-increased portion, a diameter-reduced portion and a male thread portion in turn, the male thread portion being diametrically smaller than the diameter-reduced portion; an annular-shaped pressure sensor inserted into an outer surface of the diameter-reduced portion; an annular flange inserted into the outer surface of the diameter-reduced portion to sandwich the pressure sensor with an overhang portion of the diameter-increased portion; a gasket ring being placed underside of the flange when the metallic shell is screwed through the thread portion to a cylinder block of an engine; the annular flange extending its inner rim to position at a central side of the pressure sensor, and welded to the metallic shell.