Thread: Deck flatness specification?

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On page 75 of his book, Gaskets and Gasketed Joints, author John Bickford has a table showing the “maximum out-of-flat amounts” for internal combustion engines. For V8 engines he recommends .004” in the length and .002” in the width of the gasketed surface. (This is a well-known 20 year old college level text book typically used by mechanical engineering students – Sells in the $250-$300 range on line!) He also has this note;

“This is the sum of the values of the cylinder head plus block combined. Since cylinder blocks usually do not display major out-of-flat conditions, out-of-flat conditions are usually associated with the cylinder head; but the sum of the two must be kept in mind and must not exceed the recommended specification.”

That said, I have seen factory GM blocks that measure 9.020” - 9.027” with as much as a .003” variance corner-to-corner. I still use a carpenter’s framing square and feelers (like the long one below) but have used a deck bridge with a dial caliper from time-to-time if I think there’s an issue. I’ve put a lot of engines together with Fel-Pro 1010 (.039) and 1003 (.041) gaskets that were .002” - .003” off corner-to-corner and never had problems. To Denny’s point, the 60 to 120 micro inches Ra is important and too smooth for Chevy small block can be a problem. It might be ok for aluminum Japanese engines, but cast iron should be a bit rough.

I have a lot of measuring tools – but I have consistently used these guys a lot. Inside and outside calipers, straight edges, feelers from .001” to .025”, a manual caliper (I have a digital one as well – but like this one), a lighted 10X loupe (great as the eyes age!) and my prize position the 1” micrometer that was my fathers and is more than 70 years old – still smooth as butter and dead accurate.

Keep us posted!
Glenn