Thanks For your response. I don't know how much lift I'm getting on the cam. Don't know too much about the technical aspect of this motor. Could there be a problem with the cam? The motor was rebuilt in 1985/86 (almost 300,000 mi. ago) by Vern Adair of Volpar. The only internal part on the motor that has been replaced was the timing gear, from phenolic to a metal. This is the 2nd aftermarket fp I've installed. The first one was made by Scantech, I believe,and the one in the engine now I bought from Fcp. Since the motor was rebuilt, and prior to these last fps, i really don't remember having any problems with the fp. Would a fp for a 544 be a solution? Seems like the actuating arm is shorter and may cause less stress and vibration. Thank you.