I asked about this in another thread early this mouth. I had my 71 445 rebuilt with G heads. My engine builder which is my uncle a very experienced chevy engine builder built the engine. Now reason for the build was I raised the rpm to high a started hearing what was pistons slapping in the cyclinder other than that engine ran very well. Engine builder suggested do a basic rebuild only bore .30 everything internal new with .30 over piston. First thing we notice is the engine had been torn down before and it did not have a vally pan in it. Now once the engine cam back form machine shop everything build and put back in the car we started hearing what sounded like a ping pong ball over the #3 cyclinder. Well make a long story short after days of builder test driving and listening to engine. He knew he had put a vally pan back in during this current build and he pulled these two black blocks from between the intake gasket and head gaskets they had marks where the where hitting the rocker arms during cycling. Engine builder only told me the blocks were hitting the rocker arms WHAT IN THE HELL ARE THESE BLACK BLOCKS FOR AND WHAT ARE THEY CALLED BUT EVERY SINCE THEY WERE REMOVED THE ENGINE RAN LIKE A DREAM EXCELLENT POWER FOR A STOCK BUILD MASSIVE AMOUNTS OF TORQUE

 

Hmmm, not sure about this but it sounds like they may have been exhaust crossover blocks. They are an aftermarket device that some people use to prevent heat transfer under the carburetor.

 

pix?

 

you sure he said rocker arms,seems unlikely.glad to hear it was a easy fix.

 

Blocks?

As in objects of roughly rectangular shape, with all three dimensions roughly similar in magnitude?

Made out of what? Metal? Plastic?

I am trying to understand.

- Eric

 

If they are the heat riser block-off blocks,they would be inside the crossover port of the head,and would not be anywhere near the valvetrain.

 

Good Call, Brian... I was trying to figure this one out too.

 

I'm still trying to figure out how they got out - and to the rocker arms???
I've heard of 'Gremlins", but that's a good one!
Maybe they were loose, and felll out when the manifold was pulled??