[JLMounce]

Is that even possible in a Pontiac? Even if the rear plug wasn't there?

The end play is determined by the relationship of the cam gear and eccentric (or spacer) to the cam plate and it's thickness. It's essentially held in at the front of the engine. I suppose if the eccentric was left off and the cam plate was thin, you could cause an excessive amount of end play. I don't know if that would create a near rhythmic tapping though. I would think it would be easy to see a lot of wonder in the timing if that was the case though.