Here is a head scratcher for the logical thinking bunch.

My freshly built 455 has a tapping noise coming from the passenger side bank area seemingly from the area of the 2 rear cylinders. This tapping noise is SLOWER than the actual RPM of the motor by about 1/4 to 1/2....ie, the motor idles around 800 and the tapping is around 2-400 taps per min. I located a broken inner valve spring, replaced it and now the motor idles around 5-600, Why?

The rocker is not too tight, there was a new valve stem seal installed.

My questions are these:

What are some possibilities on the noise?

Why did my motor change idle speed?

Any other insight will be greatly appreciated.

Thanks to all who have given so freely of advice, it has been a great resource for me.

Thanks
David