Detector for top dead center position of a piston for automobile engine

Claim 1

A detector for detecting when a piston, which is movable in a cylinder of a motor vehicle engine with the cylinder having a threaded opening therein for receiving an ignition plug, is at top dead center position, said detector comprising: a cylindrical body having an opening at the top portion thereof and an opening at the lower portion thereof said body having a passage therethrough having a large internal diameter at the upper portion and a small internal diameter, relative to said large diameter, at the lower portion, said body having threads on the outside around the lower portion thereof for being screwed into the ignition plug opening of a cylinder of an engine; and valve means including, (a) a check valve having a downwardly protruding shaft, said shaft having a square cross-section and a bore which extends through the center along the length thereof and branching into openings on each respective surface of said shaft at the point where said shaft is attached to said check valve, said bore and branched openings defining a vent passage within said smaller diameter portion of said cylinder body passage, (b) a valve seat located within said cylinder body passage between said smaller and larger diameter portions for cooperating with said check valve for closing off the passage between said openings at the ends of said cylinder body, (c) a valve top part mounted on the top surface of said check valve, and (d) spring means having securing means for securing said spring means in position in said large internal diameter portion and positioned for engaging said valve top part for exerting a predetermined amount of force on said check valve for maintaining said valve means closed, said valve means mounted within said cylindrical body at a location between said large diameter portion and said small diameter portion, said valve means opening for allowing air to be exhausted through said cylinder body from the cylinder on which the detector is being used, as the piston moves to top dead center position in the cylinder, and said valve means closing once the piston in the cylinder has reached the top dead center position for preventing flow therethrough from the larger diameter portion to the smaller diameter portion and for creating and maintaining a vacuum as said piston begins to move away from top dead center position for maintaining the piston at top dead center position, whereby the top dead center position of the piston can be detected.