Has anyone measured a deck height of more than 10.68 inches , mine seems to be closer to 10.75.
Crank centerline to deck

There is a fairly wide range of deck measurements I've made over the years. Yes. There can be a large variation in Deck machining. I've seen variation in other components as well. The factory crank-throw timing isn't universally accurate. As output is increased, this becomes an issue. Depending on your goals, there are tighter measurement tolerances that need to be observed, directly proportional to performance goals. All prior to bolting things together.

When building a high compression engine the first step is to verify the combustion chamber alignment to the bores. These, sometimes, aren't accurately postiioned where it comes to the factory build. Correct as necessary. Super easy when you have the bare block and head. Bolt the head to be used onto the block with alignment dowels in place, flip the block over and look down the bores to see where the combustion chambers locate to the bores. Try more than one head. Try more than one block with any given head. It might surprise you with what you observe.

Once you have the short block together, measure how far down the hole your pistons sit. (Measure more than one!) Use the pistons that you intend to use, as compression heights vary based on Vendor, overbore and other factors. Deck the block to suit. When you measure combustion chamber size, measure all of them. I've had variations both getting larger as I move from one end of the head to the other, and had the center chambers larger or smaller than the outside chambers. If your stuck with a head that has variation, average those numbers, or have the head corrected where possible. It all depends on what you want the engine to do. This is critical for performance applications, so the level of concern only increases as engine performance and compression levels head up the expectation ladder. If your going to cut the deck and/or head, don't forget to measure push rod length.

I've cut as much as 0.125" off a pump gas slant block as well as cut the head a lesser amount to get compression into range where the engine was to live. That number worked with the stroke, rod length, compression height, fuel and cam selection for my specific use and desired engine speed. Each build will need something different. There is no one recipe that fits all.

Measure, measure again, and then take a measurement. If you aren't sure, or the numbers keep changing, consult a machinist. I've built a lot of engines, and have a solid set of machine tools and measuring devices. I still take, or pay for the input of a second set of eyes to be sure for some builds. It feels great when my measurements are verified. Conversely, it saves me a metric ton of dollars when they catch something I didn't. keep in mind that if your build isn't going for nose-bleed targets, this becomes less critical, but should be as close as possible for longevity and function. A machinist's tenth is a long leap from a thou.

You likely already know all this since you took the time to measure the deck, but for the other budding mechanic that reads this thread who's still lining up his cam with the marks on timing gears, there it is.
More than you asked, but figured it might save time, money, and broken parts.

CJ

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Great answers there, CJ.

I would say 10.75" is a fairly typical number. The factory spec piston-deck height is 0.141", but most shortblocks ended up around 0.180 - 0.200" from the factory, at least for mid-60s to mid-70s. I've seen up to 0.220" on some shortblocks though. The later cast-crank shortblocks I've seen are closer to the factory spec.

Lou

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Home of Slant6-powered fun machines since 1988

Yep, pistons are .220 in the hole . So more than what you usually see . That’s why I checked the block height . Did a little research and all I could find was 10.68 , thanks for the reply and the info, Cj and Lou .

Yup. I was disappointed to measure my pistons in the hole 0.185 in the hole even after I had 0.030 milled off the deck, when spec says that's where they are supposed to have been originally new from the factory. So given that I was expecting to see them wind up closer to "only" 0.150ish when I measured upon reassembly. But I wasn't taking it all back apart to send it back to the machine shop again at that point. I also had 0.070 taken off of the head and even after all that I wound up exactly at blueprint spec of 8.4:1 compression ratio. I was hoping for closer to 9:1.
Actual deck height from crank to deck was something I honestly didn't measure

Luckily I haven’t ordered any parts yet, was just doing the math for the expected compression ratio.
Cc’d the head and it was 56 instead of the quoted 60. Nothing has matched up to factory spec yet.

The head I have started with 60cc after a 70-thou shave, 4 chambers came out at 50cc, and 2 at 49

Head cc's also vary quite a bit. Typical is 56-60, but it can be higher or lower by a few cc's.

I ALWAYS measure the piston-deck distance at TDC before I take any old engine apart. Makes planning/buying much easier and more predictable, and it is a dead simple measurement with a dial caliper. I believe almost always the variation is from crank-deck distance machining differences.

Lou

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Home of Slant6-powered fun machines since 1988

I guess I am stupid, how do you guys measure deck height?
I always measure from top of the deck to the piston.
This 10.xxx inch number is new to to me.

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Hyper_pak

You need a long caliper like this

Then measure from the pan rail to the top of the cylinder head / block to determine the deck height.
For example a G block would have ~1" shorter deck height compared to an RG 198/225 Block.

Greg

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It's about 1.5" different between 170 and 225, and I cannot recall the exact number. According to my records, it is 1.68" different. That is, the 170 block has a 9.000" spec for the crank-deck dimension and 225/198 blocks have 10.68".

The factory always went higher than those numbers to account for variations and not produce engines that would ping/detonate even on the crappier and more variable fuels of yesteryear.

Lou

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Home of Slant6-powered fun machines since 1988

??

I thought the number they are tallking about ( 10.6_?) was from the centerline of the crankshaft to the top of the deck?

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12.70 @ 104.6

Yes that seems to make more sense, Rick.
I am not sure which one it is officially?

Other sages please confirm.

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Crank centerline to top of deck. In some engines (not the Slant), these are the same.

I think ours is called a "deep skirt" block because of the pan rail being below the crank centerline. Not sure of that terminology, tho.

Lou

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Home of Slant6-powered fun machines since 1988

That's the deck height from the crank centerline. Some machine shops use that number for exact dech height.

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