4.2 L “constant tapping.

[Tree top flyer]

My rebuilt (4500 miles) engine has developed a Tapping sound in the last 100 miles. I removed the manifolds and replaced the gasket. I added a can of “Chrome- Moly, to free up any potential stuck lifters. Still have the tapping. It still sounds like an exhaust manifold leak.
Will doubling up on the manifold gasket be a good idea to stop the problem??

 

[Flyer58]

Hopefully the exhaust manifold isn't cracked. You can check to see if the gasket was blown out but since the tolerance is so close, I doubt two gaskets will help. One gasket should do it. My 2.4L doesn't even have an exhaust gasket from the factory, just steel against steel.

As a friendly reminder, make sure you tighten the exhaust nuts in the proper sequence to avoid leaks or cracks.