Importance

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Abstract

In an overhead cam internal combustion engine, an adjustable thickness shim assembly is interposed between the end of a valve stem and the underside of a conventional inverted cup follower engaged by the cam shaft. A body component of the shim assembly forms a ramp for a tapered wedge component which is slidable along the ramp to adjust the effective thickness of the shim. The body component has an inclined threaded bore adjacent to the wedge component receiving a screw which when turned advances along the ramp to butt against the wedge component. The body component is formed of a material having a higher coefficient of thermal expansion than the screw such that when the engine is cold the screw is pinched in its bore and will not turn. When the engine is warmed to normal operating temperature, the body component expands to a greater degree than the screw and the screw is free to turn. The bore and screw are positioned such that inertial force exerted on the screw by movement with the valve stem tends to advance the screw toward the edge component so as to adjust the valve clearance automatically.

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First Claim