Originally Posted by david-b
Tech, makes perfect sense. Would have never thought of that. I don't remember the exact shave done by remember it was very little.
Just so everyone reading this is clear on what I'm saying, that's not the head surface I'm talking about. You're saying the shop took a slight skim off the block mating surface of the heads, probably just to make sure it was parallel and would hold a head gasket. The surface I'm talking about is the intake manifold mating surface that was cut by the head manufacturer at the time of manufacture. It could be off by any number of degrees or it could be dead on the money, matching the intake manifold mating surface exactly. Also, consider that the block being machined lolly-gagged could result in the same problem. If one end of the block is higher than the other, (example: block deck height on one bank at the front of the block measures 9.016". Block deck height on the other bank at the front of the block measures 9.026") then when you bolt the heads on, one head is higher than the other and no matter how true the head/manifold mating surfaces are, there is no way in hell that the manifold will seal up to the heads. You have to begin with cutting the block decks on a Tru-Deck mill, exactly 90 degrees apart and exactly parallel with the main bearing bore.
And of course, the heads could be dead-nuts on the money, but the intake manifold could be cut askew. Like I said above, sacrifice a set of gaskets and verify the seal yourself.