Piston top dead center locating tool

Abstract

A tool for visually indicating the relative crankshaft and piston position at top dead center for an internal combustion engine of the type having a threaded opening for a spark plug positioned above the piston's top surface. The tool consists of a base which has threads for attachment in the spark plug opening, an outer tubular member supported by the base to allow it to slide upward through the base in response to urging of the top of the piston moving toward the base but otherwise being frictionally secured to the base, and an inner member equal in the length dimension to the outer member and supported by the outer member in a manner allowing it to initially move upward with the outer tubular member as urged by the piston but also allowing it to move with the piston away from the base and the outer member whereby changes in the alignment of the exterior ends of the members indicates piston movement past top dead center.

What is claimed is: 
     
       1. For an internal combustion engine having an axially aligned cylinder and spark plug aperture in a cylinder head, a top dead center position indicator for a piston in the cylinder, comprising: a base member with a threaded end portion adapted to be attached to the engine within the spark plug aperture to provide a stationary support, said base member having a bore therethrough with an axis generally aligned with the axis of the cylinder; a tubular outer member extending through said bore in said base member; an inner member supported within said tubular outer member, said inner member being capable of reciprocal movements within said outer member; said outer member being sized relative to said bore in said base member to permit reciprocal movement of said outer member relative to said base member only in response to a significant axially applied force upon the outer member, as by upward movements of the piston toward the base member; said inner member being sized relative to said tubular outer member to permit free reciprocal movements within said outer member; said tubular outer member and said inner member having exactly the same length dimension so that as the ends nearest the piston of said outer and inner members are contacted by a piston as it moves in the cylinder toward said base member, the opposite externally exposed end surfaces of both members are arranged to form a common unbroken plane and subsequently as the piston moves oppositely away from the base member, only the inner member follows the movement of the piston thereby producing a visual axial dislocation of said end surfaces to visually present the ends in two different planes. 
     
     
       2. A piston position indicating tool for revealing the top dead center position of a piston in a combustion chamber of an internal combustion engine of the type having a cylinder bore and a cylinder head with a threaded spark plug opening, the spark plug opening and the cylinder being generally axially aligned with direction of travel taken by a piston in the cylinder, comprising: a base member having an end portion with external thread means configured and sized to attach into the spark plug opening for temporarily attachment to the engine, said base member having a bore therethrough with its axis extending generally parallel to the movement of the piston in the cylinder; a tubular outer member extending through said bore in said base member and defining an interior end portion adapted to project into the combustion chamber of the associated engine and having an opposite exterior end portion; an inner member supported by and extending through said tubular outer member, said inner member having an interior end portion within the combustion chamber of the associated engine and having an opposite exterior end portion; said outer member being sized and configured relative to said bore in said base member to permit axial movement of said outer member relative to said base member only in response to a significant axially applied force upon said outer member such as by upward movement of the piston toward said base member; said inner member being sized and configured relative to said supporting tubular outer member to freely allow axial movement relative to said outer member and said base member without significant axially applied forces other than gravitational force; said tubular outer member and said inner member having equal lengths so that when the interior ends of both members are engaged by a piston moving upward toward said base member, said opposite external ends of both members are arranged to form a common unbroken plane but when the piston moves past its top dead center position and withdraws from said base member, said outer member retains its uppermost position relative to the base member while the inner member follows the piston's downward movement thereby producing an axial dislocation of said external end surfaces to visually present the outer and inner ends in two different planes. 
     
     
       3. The piston position indicating tool as set forth in claim 2 in which the internal end portion of said outer member is furnished with a beveled end configuration so as to contact the top surface of an associated piston immediately adjacent the end surface of the inner member.