1972 SB deck height

[Jerome P.]

The spec'd height of a SB block (350 ci) I believe is 9.025". Does anyone know what the +/- tolerances that were allowed before the block was rejected?

[Jerome P.]

Re: 1972 SB deck height

Somebody must know the answer. Maybe Duke!!!

[Clem Z.]

Re: 1972 SB deck height

every block i ever check was .010/.015 over. never saw any under

[Duke W.]

Re: 1972 SB deck height

I don't know what the tolerance is on the print. Clem has measured a a lot more deck heights/deck clearances than I have, and my results are the same as his. Most are high up to .015". I've run across one that was right on - at least on one side.

It's also common to see .005-.010" difference side to side.

High decks are the primary reason why actual as-built compression ratios are less than advertised.

It doesn't appear they ever rejected or reworked a block because the decks were high, and I have no idea how often they came out low.

The wide variation in deck height/deck clearance is why I harp on it and co-wrote an article about it in the Fall 2009 Corvette Restorer. CR is a very important parameter to achieve maximum performance and fuel economy, and it's not that hard to "manage" starting with measuring deck clearance on all eight when you tear down an engine for restoration.

Do you have any measurements, Jerome?

Duke

[Jerome P.]

Re: 1972 SB deck height

My deck height at #1 measured at 9.020" and 9.028" at #2. From front to back each side varied from the 1 and 2 cylinders +\- .002" at the other cylinders. I am surprised there is no history of a unit having a minus tolerance from the spec'd deck height.
Does anyone else have any thoughts or comments?

Any other experiences with the other block sizes? 283, 327, 396, 427, 454 etc?

[Clem Z.]

Re: 1972 SB deck height

My deck height at #1 measured at 9.020" and 9.028" at #2. From front to back each side varied from the 1 and 2 cylinders +\- .002" at the other cylinders. I am surprised there is no history of a unit having a minus tolerance from the spec'd deck height.
Does anyone else have any thoughts or comments?

Any other experiences with the other block sizes? 283, 327, 396, 427, 454 etc?

how did you measure this? the correct way is to use the same rod and piston combination in all 4 places because there can be a difference in rod length and compression distance on the piston. back in the day when you had to have all stock parts in drag racing i would measure the rod length,the piston compression distance and the crank throw length separately and match parts so the deck clearance would be a close as possible on all cylinders. this is one of the problems that the first olds diesels had was a stack up of machine tolerances and the compression ratio between cylinders was different.

[William C.]

Re: 1972 SB deck height

You have to remember the manufacturing process, the mains and decks were cut in one process using a huge broach. Too much metal off the top would result in a scrapped block, something to be avoided, so the process was set up to be on the "Safe" side, err on the side of caution.