I thought I'd post this for all to see. This was done on a standard bore 455 but it applies to all blocks.
It's been mentioned many times to "sonic check" the block before proceeding in any given build. However I'll bet many don't have it done.

Here's the sonic check sheet for a 455 build I'm doing for another member on here. Although the thinnest area is not on a thrust side, I think all would agree boring this block to .060, or even .030 over could cause a problem. At that point you're potentially left with a cylinder thickness of less than .080. Imo that's totally unacceptable in most if not all cases. A thin area in virtually any part of the cylinder wall will allow it to flex more than normal and adversely effect ring seal as well as overall longevity.
Needless to say, I'm not going to use this block. Hope this helps.


Note cyl#3 especially. Thanks.

 

I'd be thinking bore and sleeve it.

 

Yes maybe but is the cost worth it? Not sure. And you have another questionable one that isn't much thicker.

 

Wow!

Just out of curiosity, what's the year of this block?

 

'73, numbers are the side are 35M16962something. Last number is all scratched out.

 

35M would be 1975. The 3 is for Oldsmobile.

 

Yeah after I posted that I knew I switched up the numbers, sorry.
Nonetheless I hope I made my point, spend the $80-$90 and have it done.

 

It would be interesting to track wall thickness vs. year of manufacture. THAT would be a meaningful distinction (as opposed to "nickel content"...).

 

Wall thickness by year yields no given pattern. I've seen thick and thin in all if the years of BBO. It all has to do with how well the pattern was put together and the mold built around it.
Another factor is just where the first cut off of the block was taken and what it was referenced to. Everything is machined off the first surface cut. If it wasn't referenced to a specific point on the casting then all machine work is going to be centerd or not in the casting. I think this to be the reason most blocks have one side or the other of the bores much thinner than the other.

 

I figured as much. I was just wondering if there was a conscious move to thinner walls to reduce weight in the 1970s. Probably not on the existing BBO castings, though. More likely that happened in conjunction with windowed main webs.

 

Good info Mark and Smitty, thanks.

 

I recently checked mine by hand with a long reach dial caliper through the water jacket cooling holes. I realize it's not the preferred method but I couldn't justify the cost of sonic testing it or purchasing the test equipment.
My block is currently .060 over and I never got a reading less than .240 anywhere I checked it. The range was .240 - .280. It should be noted this was in the diagonal positions so it's a little biased away from the ideal measuring points like yours is.
Looking at your chart you can see that the thinnest spots are always at 3 and 9 o'clock and the thickest are 12 and 6 o'clock. 12 and 6 o'clock would be the thrust side depending on whether it's the left or right side of the block. I've studied this and everything I've read said that as long as the thrust side isn't under .180 you'll be fine. Some even state a lower figure. I'm no expert here but I think your fine.

 

The 1968-69 had the thick wall. I have a motor that we bored .165 over and used Big Block Chevy pistons in. Back in 1986. Had to work with the carbs with bigger jets but it ran around 200 degrees all the time. It had over 5000 miles on before we pulled it and put a small block Olds in. About 7.5 to 1 compression.
In 1970 they made the blocks lighter. I will be weighing all 3 F blocks(F,F, Fa later on.
There are a couple guys that have done this here in the Midwest.
Mike

 

Is this the same as sbo or is it because the bbo are bigger therefore less material is used to cut weight?

 

I'll post some more sheets. Even the earlier blocks aren't that much thicker, maybe .020-.040 or so.
And you all are forgetting one thing. These can be bored incorrectly from the factory as well. You'll see when I post the other sheets. I had a D block and a '70 F block that had what looked like core shift when in fact they had poorly bored holes. It was evident at the top as well. It had a huge chamfer on one side with nearly a sharp edge on the opposite side.
And I believe the reference point for initial machining is taken from the dowel hole in the pan rail. But it can be screwed up from there. I've seen it more often that not.

 

Its also very possible that the locating dowel hole Mark mentioned are in the wrong location. Everything is located off the first surface cut on the raw casting. If it is not located perfectly in relation to the casting then everything will be off.I'm sure that since they never intended for us to be going 1/8 over bore that it wasn't something they worried about. In tolerance is all that counted to a guy running piece work.

 

Here are two more. Both became more concentric once they were bored with the BHJ, especially the 455. It was bored .055 over. After boring we checked cyls 4 and 6 especially. Again they were much more even afterwards with thicknesses no less than .115-.120. Conversely look how much more concentric cyls 3 and 5 are on the 455. And that showed up on the BHJ plate as well. That side cleaned up more quickly than the other side.

Trip D- notice the top measurements on the 350. See all the .300+'s? Now look below them, see anymore? Same with the 455, most all of the thickness is at the top, especially on the 455 like you have. Imo I think you missed the boat on your priorities.
The 350 is a '69, the 455 is a '70. Both will have near stock or higher rod ratios with lighter internals as well. That lessens the load on the cylinder walls.
Hope this helps.

 

So your saying the walls aren't as thin on a 350 sorry I can't make heads or tails of the numbers besides some higher than others

 

Not initially no, but that starts out with a smaller bore to begin with vs the 455.

 

Cutlassefi, why stir the pot on this and use me as an example? I've never heard of anyone having a problem at .060 on a BBO but now I have a suspect block because you think so? Besides, what I do with my money and how I want to spend it is my business. Sonic checking was not going to happen on a .060 over block in my world no matter what the cost. If it breaks then I have two more blocks ready to go and I'll start over. There is also a lot more than the thinnest wall supporting that cylinder. You have the deck and main area not to mention water pressure from the cooling system ( I wouldn't put my money on this but I added it anyway). Did you also check the walls from top to bottom in half inch increments or just took the reading from the center of the bore? Maybe the tech just moved the transducer around until he found the thinnest spot? There are a lot of variables here.
I was only trying to help and offer my experience but since you've decided to make me a target you can pound sand. Anyone who's read these forums long enough knows you have an agenda and it mostly involves two topics: What to use as a reference point when machining a block and water temps. on dyno pulls. You can also add in cam selection. I already know you don't like my choice there either.
Stick to bickering with the other knowledgeable engine builders and so called Olds experts but lay off the little guys like me. I can bite back just as hard.

 

You're right it's your money. Spend it as you please. However you offered up how you measured yours, acknowledging that it probably wasn't very accurate. I supported that claim and offered my OPINION, supported by facts, plain and simple. Don't shoot the messenger.

Best of luck in your build.

 

Ok that makes sense

 

Geez Trip, calm down and don't bite anybody. After all you wouldn't even pay to have your block sonic tested the right way.

 

Says it all:

 

The more I see, the more I think bore and sleeve and your worries are behind you. Does anyone have real world numbers for that? I mean, if you're going to have to buy 3 blocks and sonic each one to get you to where you're confident, ...?

 

The success of any engine is the right clearances and attention to details. Sonic testing is one of those details.

 

Even if you use block filler it wont help? Just curious.

 

Filling the block makes worlds of difference as to what is acceptable. I worry about what will be exposed. Not about what will be backed by the block filler. Within reason of course. There would still be a limit as to what I'd accept.

 

I don't think it makes worlds of difference. You are only filling the block to the bottom of the water pump holes. Most usually the thin spots are up towards the top. The main reason for block filler is to keep the cylinders round.

 

You have it totally backwards Nick. The thin areas are at the bottom 99% of the time. I've sonic checked more than enough blocks to back that up.

 

Sorry but the blocks I've had checked, the thin spots were up towards the top. I won't argue with you, after Josh's deal I'm outa here.